Willy Loman returns home exhausted after a cancelled business trip. Worried over Willy's state of mind and recent car accident, his wife Linda suggests that he ask his boss Howard Wagner to allow him to work in his home city so he will not have to travel. Willy complains to Linda that their son, Biff, has yet to make good on his life. Despite Biff's promising showing as an athlete in high school, he flunked senior-year math and never went to college.
Biff and his brother Happy, who is temporarily staying with Willy and Linda after Biff's unexpected return from the West, reminisce about their childhood together. They discuss their father's mental degeneration, which they have witnessed in the form of his constant indecisiveness and recurrent instances of talking to himself when he thinks he is alone. Willy walks in, angry that the two boys have never amounted to anything. In an effort to pacify their father, Biff and Happy tell their father that Biff plans to make a business proposition the next day.
The next day, Willy goes to ask his boss, Howard, for a job in town while Biff goes to make a business proposition, but both fail. Willy gets angry and ends up getting fired when the boss tells him he needs a rest and can no longer represent the company. Biff waits hours to see a former employer who does not remember him and turns him down. Biff impulsively steals a fountain pen. Willy then goes to the office of his neighbor Charley, where he runs into Charley's son Bernard (now a successful lawyer); Bernard tells him that Biff originally wanted to do well in summer school, but something happened in Boston when Biff went to visit his father that changed his mind.
Happy, Biff, and Willy meet for dinner at a restaurant, but Willy refuses to hear bad news from Biff. Happy tries to get Biff to lie to their father. Biff tries to tell him what happened as Willy gets angry and slips into a flashback of what happened in Boston the day Biff came to see him. Willy had been having an affair with a receptionist on one of his sales trips when Biff unexpectedly arrived at Willy's hotel room. A shocked Biff angrily confronted his father, calling him a liar and a fraud. From that moment, Biff's views of his father changed and set Biff adrift.
Biff leaves the restaurant in frustration, followed by Happy and two girls that Happy has picked up. They leave a confused and upset Willy behind in the restaurant. When they later return home, their mother angrily confronts them for abandoning their father while Willy remains outside, talking to himself. Biff tries unsuccessfully to reconcile with Willy, but the discussion quickly escalates into another argument. Biff conveys plainly to his father that he is not meant for anything great, insisting that both of them are simply ordinary men meant to lead ordinary lives. The feud reaches an apparent climax with Biff hugging Willy and crying as he tries to get Willy to let go of the unrealistic expectations. Willy still clings to high expectations for him and cannot accept him for who he really is. He still cannot confront his son about his own moral lapses and indiscretions and weeps while he prepares to go to bed, exhausted. Willy, "astonished," says, "Biff - he likes me." Linda comforts him and tells him, "He loves you, Willy."
Rather than listen to what Biff actually says, Willy appears to believe his son has forgiven him and thinks Biff will now pursue a career as a businessman. Willy kills himself, apparently intentionally by crashing his car so that Biff can use the life insurance money to start his business. The ambiguities at the funeral of mixed and unaddressed emotions persist. At the funeral Biff retains his belief that he does not want to become a businessman like his father. Happy, on the other hand, chooses to follow in his father's footsteps.