Nineteen-year-old Roy Hobbs, a country bumpkin with a great pitching arm, is on his way to Chicago to try out for the Chicago Cubs. He is on the train with the Cubs' scout, Sam Simpson. While on the train, Roy meets a woman named Harriet Bird, for whom he immediately develops a crush. He also meets a sports journalist, Max Mercy, who is on the train with a famous baseball hitter, the Whammer.

The train stops at a carnival, and Roy and the Whammer both show off their skills at games. Sam bets that Roy can strike out the Whammer, and Roy does. In the process, however, Roy accidentally hurts Sam, who dies later that day from the injury. When they reach Chicago, Harriet invites Roy to her room. After Roy tells her he will be "the greatest in the game," she shoots him.

Fifteen years later, Pop Fisher, the manager of the New York Knights, discovers he has a new "rookie" for his team—a thirty-four-year-old man named Roy Hobbs, whom the team's owner, the stingy Judge Banner, has signed for a paltry $3,000. The Knights are doing very poorly; even their playing field is dried up from a long drought.

Pop is skeptical of Roy. When Roy refuses to join the hypnotist sessions to which Pop subjects the team, Pop benches Roy for three weeks. In the meantime, Roy falls for Pop's niece, Memo Paris, but she is already the girlfriend of the team's star player, Bump Baily. Roy also meets Max Mercy, the sports journalist, again, but Mercy does not recognize him.

Finally, Pop sends Roy into a game one day to pinch-hit. Roy smashes the cover off the ball on his first at-bat, and at the same time a downpour begins that lasts for three days. Soon, the field is green again and Roy is hitting regularly, wowing everyone with his amazing talent. Bump Baily takes offense at Roy's rise, and he tries so hard to outdo Roy that he accidentally cracks his skull against the wall. Bump later dies from his injuries; ultimately, Roy tries to move in on Memo. She is cold and indifferent to him, but he cannot stop thinking about her.

When the Knights begin to rise in the standings due to Roy's amazing performance, Roy asks the Judge for a raise, but the Judge refuses. Roy runs into Max Mercy, who takes him out to a club owned by Gus Sands, the "Supreme Bookie"—a millionaire tycoon of the betting circuit. Gus and Memo are sitting together when Roy and Max arrive. Gus wins some significant money from Roy, and Roy pays him back in the form of parlor tricks.

A few weeks later, the fans hold "Roy's Day," in which they shower him with cheers and gifts after hearing how poorly the Judge has been treating him. Roy even gets a car and takes Memo on a date. The date goes poorly, however, and Roy ends up crashing the car into a ditch. Neither of them are injured, but it is clear that Memo is not very interested in Roy. Nevertheless, he cannot stop obsessing over her.

Shortly thereafter, Roy enters a slump, unable to get a single hit. He tries everything he can to end the slump, from superstitious tricks to meeting a fortuneteller. Pop tells Roy to stop using his bat, Wonderboy, and to try a different one, but Roy refuses. Just before a game in Chicago, a fan begs Roy to hit a home run; the fan told his son, who is fighting for his life in the hospital, that Roy said he would. Pop lets Roy bat, and Roy immediately goes through two strikes. Then Roy notices a woman standing up in the crowd for him. The woman gives him a kind of strength, and he nails a home run on the next hit.

Roy decides to meet the woman. Her name is Iris Lemon. The two go on a date, and Iris seems to understand Roy very well. Unfortunately, Roy does not seem to understand Iris or what she is trying to tell him. They go swimming and then make love, but Roy is shocked to discover that Iris, at age thirty-three, is already a grandmother. He soon tries to forget about her, focusing once more on Memo, who has ignored him for weeks.

Suddenly, as Roy is hitting well again, Memo begins to pay attention to him, making him hunger for her even more. But he also hungers for vast amounts of food, and he begins to eat and eat. Memo holds a great banquet for all the players before an important three-game series, promising Roy sex after the banquet. But when Roy goes to her, he gets an enormous stomachache and winds up in the hospital.

Meanwhile, the Knights lose their next three games, tying the Pirates for first place. Memo visits Roy at the hospital. He asks her to marry him, but she tells him she cannot do so unless he is sufficiently rich and can "take care of her." Shortly thereafter, Judge Banner visits Roy and offers him $35,000 to throw the next game, which will decide who wins the pennant. Roy reluctantly agrees, and the next day at the game, he does not play his best.

However, Roy slowly begins to change his mind. At one at-bat, he is viciously booed by a dwarf named Otto P. Zipp. Roy tries to foul off several pitches toward the dwarf; one finally hits the dwarf, but caroms off the dwarf's skull and hits a woman that had stood up in the stands—Iris Lemon. Iris tells Roy that she is pregnant with his child, and that he must win the game for both the child and the two of them. Roy agrees and goes back to the plate ready to crack one. But as he does so, his bat, Wonderboy, splits in half.

In his next at-bat, Roy is once again ready to conquer, though not with Wonderboy. The opposing team's pitcher is so terrified of Roy that he faints dead away. The other team sends out a young phenom pitcher instead. Roy suddenly finds himself in the place of the Whammer, striking out against a young, fantastic pitcher. Distraught after the game, Roy visits the Judge and beats him up, along with Gus Sands. Roy throws the Judge's money at him and calls Memo a whore. Memo tells him that she has hated him ever since he "murdered Bump." Roy leaves and sees a newspaper: Max Mercy has discovered Roy's sellout. A boy asks Roy, "Say it ain't so, Roy." Roy can only weep in response.