Scopes was found guilty and fined $100 (equivalent to $1,500 in 2020), but the verdict was overturned on a technicality. The trial served its purpose of drawing intense national publicity, as national reporters flocked to Dayton to cover the big-name lawyers who had agreed to represent each side. William Jennings Bryan, three-time presidential candidate and former Secretary of State, argued for the prosecution, while Clarence Darrow served as the defense attorney for Scopes. The trial publicized the Fundamentalist–Modernist controversy, which set Modernists, who said evolution was not inconsistent with religion, against Fundamentalists, who said the Word of God as revealed in the Bible took priority over all human knowledge. The case was thus seen both as a theological contest and as a trial on whether modern science should be taught in schools.
State Representative John Washington Butler, a Tennessee farmer and head of the World Christian Fundamentals Association, lobbied state legislatures to pass anti-evolution laws. He succeeded when the Butler Act was passed in Tennessee, on March 25, 1925. Butler later stated, "I didn't know anything about evolution ... I'd read in the papers that boys and girls were coming home from school and telling their fathers and mothers that the Bible was all nonsense." Tennessee governor Austin Peay signed the law to gain support among rural legislators, but believed the law would neither be enforced nor interfere with education in Tennessee schools. William Jennings Bryan thanked Peay enthusiastically for the bill: "The Christian parents of the state owe you a debt of gratitude for saving their children from the poisonous influence of an unproven hypothesis."
In response, the American Civil Liberties Union financed a test case in which John Scopes, a Tennessee high school science teacher, agreed to be tried for violating the Act. Scopes, who had substituted for the regular biology teacher, was charged on May 5, 1925, with teaching evolution from a chapter in George William Hunter's textbook, Civic Biology: Presented in Problems (1914), which described the theory of evolution, race, and eugenics. The two sides brought in the biggest legal names in the nation, William Jennings Bryan for the prosecution and Clarence Darrow for the defense, and the trial was followed on radio transmissions throughout the United States.
The American Civil Liberties Union (ACLU) offered to defend anyone accused of teaching the theory of evolution in defiance of the Butler Act. On April 5, 1925, George Rappleyea, local manager for the Cumberland Coal and Iron Company, arranged a meeting with county superintendent of schools Walter White and local attorney Sue K. Hicks at Robinson's Drug Store, convincing them that the controversy of such a trial would give Dayton much needed publicity. According to Robinson, Rappleyea said, "As it is, the law is not enforced. If you win, it will be enforced. If I win, the law will be repealed. We're game, aren't we?" The men then summoned 24-year-old John T. Scopes, a Dayton high school science and math teacher. The group asked Scopes to admit to teaching the theory of evolution.
Rappleyea pointed out that, while the Butler Act prohibited the teaching of the theory of evolution, the state required teachers to use a textbook that explicitly described and endorsed the theory of evolution, and that teachers were, therefore, effectively required to break the law. Scopes mentioned that while he couldn't remember whether he had actually taught evolution in class, he had, however, gone through the evolution chart and chapter with the class. Scopes added to the group: "If you can prove that I've taught evolution and that I can qualify as a defendant, then I'll be willing to stand trial."
Scopes urged students to testify against him and coached them in their answers. He was indicted on May 25, after three students testified against him at the grand jury; one student afterwards told reporters, "I believe in part of evolution, but I don't believe in the monkey business." Judge John T. Raulston accelerated the convening of the grand jury and "... all but instructed the grand jury to indict Scopes, despite the meager evidence against him and the widely reported stories questioning whether the willing defendant had ever taught evolution in the classroom". Scopes was charged with having taught from the chapter on evolution to a high-school class in violation of the Butler Act and nominally arrested, though he was never actually detained. Paul Patterson, owner of The Baltimore Sun, put up $500 in bail for Scopes.
The original prosecutors were Herbert E. and Sue K. Hicks, two brothers who were local attorneys and friends of Scopes, but the prosecution was ultimately led by Tom Stewart, a graduate of Cumberland School of Law, who later became a U.S. Senator. Stewart was aided by Dayton attorney Gordon McKenzie, who supported the anti-evolution bill on religious grounds, and described evolution as "detrimental to our morality" and an assault on "the very citadel of our Christian religion".
Baptist pastor William Bell Riley, the founder and president of the World Christian Fundamentals Association, was instrumental in calling lawyer and three-time Democratic presidential nominee, former United States Secretary of State, and lifelong Presbyterian William Jennings Bryan to act as that organization's counsel. Bryan had originally been invited by Sue Hicks to become an associate of the prosecution and Bryan had readily accepted, despite the fact he had not tried a case in thirty-six years. As Scopes pointed out to James Presley in the book Center of the Storm, on which the two collaborated: "After [Bryan] was accepted by the state as a special prosecutor in the case, there was never any hope of containing the controversy within the bounds of constitutionality."
In response, the defense sought out Clarence Darrow, an agnostic. Darrow originally declined, fearing his presence would create a circus atmosphere, but eventually realized that the trial would be a circus with or without him, and agreed to lend his services to the defense, later saying he "realized there was no limit to the mischief that might be accomplished unless the country was aroused to the evil at hand". After many changes back and forth, the defense team consisted of Darrow, ACLU attorney Arthur Garfield Hays, Dudley Field Malone, an international divorce lawyer who had worked at the State Department, W.O. Thompson, who was Darrow's law partner, and F.B. McElwee. The defense was also assisted by librarian and Biblical authority Charles Francis Potter, who was a Modernist Unitarian preacher.
The prosecution team was led by Tom Stewart, district attorney for the 18th Circuit (and future United States Senator), and included, in addition to Herbert and Sue Hicks, Ben B. McKenzie and William Jennings Bryan.
The trial was covered by journalists from the South and around the world, including H. L. Mencken for The Baltimore Sun, which was also paying part of the defense's expenses. It was Mencken who provided the trial with its most colorful labels such as the "Monkey Trial" of "the infidel Scopes". It was also the first United States trial to be broadcast on national radio.
The ACLU had originally intended to oppose the Butler Act on the grounds that it violated the teacher's individual rights and academic freedom, and was therefore unconstitutional. Principally because of Clarence Darrow, this strategy changed as the trial progressed. The earliest argument proposed by the defense once the trial had begun was that there was actually no conflict between evolution and the creation account in the Bible; later, this viewpoint would be called theistic evolution. In support of this claim, they brought in eight experts on evolution. But other than Dr. Maynard Metcalf, a zoologist from Johns Hopkins University, the judge would not allow these experts to testify in person. Instead, they were allowed to submit written statements so their evidence could be used at the appeal. In response to this decision, Darrow made a sarcastic comment to Judge Raulston (as he often did throughout the trial) on how he had been agreeable only on the prosecution's suggestions. Darrow apologized the next day, keeping himself from being found in contempt of court.
The presiding judge, John T. Raulston, was accused of being biased towards the prosecution and frequently clashed with Darrow. At the outset of the trial, Raulston quoted Genesis and the Butler Act. He also warned the jury not to judge the merit of the law (which would become the focus of the trial) but on the violation of the Act, which he called a 'high misdemeanor'. The jury foreman himself was unconvinced of the merit of the Act but he acted, as did most of the jury, on the instructions of the judge.
Bryan chastised evolution for teaching children that humans were but one of 35,000 types of mammals and bemoaned the notion that human beings were descended "Not even from American monkeys, but from old world monkeys".
Darrow responded for the defense in a speech that was universally considered the oratorical climax of the trial. Arousing fears of "inquisitions", Darrow argued that the Bible should be preserved in the realm of theology and morality and not put into a course of science. In his conclusion, Darrow declared that Bryan's "duel to the death" against evolution should not be made one-sided by a court ruling that took away the chief witnesses for the defense. Darrow promised there would be no duel because "there is never a duel with the truth." The courtroom went wild when Darrow finished; Scopes declared Darrow’s speech to be the dramatic high point of the entire trial and insisted that part of the reason Bryan wanted to go on the stand was to regain some of his tarnished glory.
On the sixth day of the trial, the defense ran out of witnesses. The judge declared that all the defense testimony on the Bible was irrelevant and should not be presented to the jury (which had been excluded during the defense). On the seventh day of the trial, the defense asked the judge to call Bryan as a witness to question him on the Bible, as their own experts had been rendered irrelevant; Darrow had planned this the day before and called Bryan a "Bible expert". This move surprised those present in the court, as Bryan was a counsel for the prosecution and Bryan himself (according to a journalist reporting the trial) never made a claim of being an expert, although he did tout his knowledge of the Bible. This testimony revolved around several questions regarding Biblical stories and Bryan's beliefs (as shown below); this testimony culminated in Bryan declaring that Darrow was using the court to "slur the Bible" while Darrow replied that Bryan's statements on the Bible were "foolish".
On the seventh day of the trial, Clarence Darrow took the unorthodox step of calling William Jennings Bryan, counsel for the prosecution, to the stand as a witness in an effort to demonstrate that belief in the historicity of the Bible and its many accounts of miracles was unreasonable. Bryan accepted, on the understanding that Darrow would in turn submit to questioning by Bryan. Although Hays would claim in his autobiography that the examination of Bryan was unplanned, Darrow spent the night before in preparation. The scientists the defense had brought to Dayton—and Charles Francis Potter, a modernist minister who had engaged in a series of public debates on evolution with the fundamentalist preacher John Roach Straton—prepared topics and questions for Darrow to address to Bryan on the witness stand. Kirtley Mather, chairman of the geology department at Harvard and also a devout Baptist, played Bryan and answered questions as he believed Bryan would. Raulston had adjourned court to the stand on the courthouse lawn, ostensibly because he was "afraid of the building" with so many spectators crammed into the courtroom, but probably because of the stifling heat.
An area of questioning involved the book of Genesis, including questions about whether Eve was actually created from Adam's rib, where Cain got his wife, and how many people lived in Ancient Egypt. Darrow used these examples to suggest that the stories of the Bible could not be scientific and should not be used in teaching science with Darrow telling Bryan, "You insult every man of science and learning in the world because he does not believe in your fool religion." Bryan's declaration in response was, "The reason I am answering is not for the benefit of the superior court. It is to keep these gentlemen from saying I was afraid to meet them and let them question me, and I want the Christian world to know that any atheist, agnostic, unbeliever, can question me anytime as to my belief in God, and I will answer him."
Stewart objected for the prosecution, demanding to know the legal purpose of Darrow's questioning. Bryan, gauging the effect the session was having, snapped that its purpose was "to cast ridicule on everybody who believes in the Bible". Darrow, with equal vehemence, retorted, "We have the purpose of preventing bigots and ignoramuses from controlling the education of the United States."
A few more questions followed in the charged open-air courtroom. Darrow asked where Cain got his wife; Bryan answered that he would "leave the agnostics to hunt for her". When Darrow addressed the issue of the temptation of Eve by the serpent, Bryan insisted that the Bible be quoted verbatim rather than allowing Darrow to paraphrase it in his own terms. However, after another angry exchange, Judge Raulston banged his gavel, adjourning the court.
The confrontation between Bryan and Darrow lasted approximately two hours on the afternoon of the seventh day of the trial. It is likely that it would have continued the following morning but for Judge Raulston's announcement that he considered the whole examination irrelevant to the case and his decision that it should be "expunged" from the record. Thus Bryan was denied the chance to cross-examine the defense lawyers in return, although after the trial Bryan would distribute nine questions to the press to bring out Darrow's "religious attitude". The questions and Darrow's short answers were published in newspapers the day after the trial ended, with The New York Times characterizing Darrow as answering Bryan's questions "with his agnostic's creed, 'I don't know,' except where he could deny them with his belief in natural, immutable law".
Scopes never testified since there was never a factual issue as to whether he had taught evolution. Scopes later admitted that, in reality, he was unsure of whether he had taught evolution (another reason the defense did not want him to testify), but the point was not contested at the trial.
After eight days of trial, it took the jury only nine minutes to deliberate. Scopes was found guilty on July 21 and ordered by Raulston to pay a $100 fine (equivalent to $1,500 in 2020). Raulston imposed the fine before Scopes was given an opportunity to say anything about why the court should not impose punishment upon him and after Neal brought the error to the judge's attention the defendant spoke for the first and only time in court: Your honor, I feel that I have been convicted of violating an unjust statute. I will continue in the future, as I have in the past, to oppose this law in any way I can. Any other action would be in violation of my ideal of academic freedom—that is, to teach the truth as guaranteed in our constitution, of personal and religious freedom. I think the fine is unjust.
Although the Tennessee Supreme Court upheld the statute as constitutional, it reversed Scopes conviction on technical grounds because the judge, not the jury, imposed the fine. At that time, only a jury could impose a fine of greater than $50. Because Scopes was not longer employed by the state, the Supreme Court simply dismissed the case rather than remand it back for a new sentencing proceeding.
In 1968, the Supreme Court of the United States ruled in Epperson v. Arkansas 393 U.S. 97 (1968) that such bans contravene the Establishment Clause of the First Amendment because their primary purpose is religious. Tennessee had repealed the Butler Act the previous year.
Bryan died suddenly five days after the trial's conclusion. The connection between the trial and his death is still debated by historians.