Billionaire media mogul William Parrish (Anthony Hopkins) is considering a merger between his company and another media giant, while also about to celebrate his 65th birthday with an elaborate party being planned by his eldest daughter Allison (Marcia Gay Harden). He begins to hear mysterious voices, which he tries with increasing difficulty to ignore.
His youngest daughter Susan (Claire Forlani), an internal medicine resident, is involved with one of Bill's board members, Drew (Jake Weber). She is considering marriage, but her father is not favorably impressed by her relationship. When she asks for the short version of his impassioned speech, he simply says, "Stay open. Who knows? Lightning could strike!" Shortly thereafter, Susan meets a vibrant young man (Brad Pitt) at a coffee shop. She is instantly enamored but fails to even get his name. Minutes after their encounter (and unbeknownst to her), the man is struck by multiple cars in what appears to be a remarkably serious motor vehicle accident.
The grim reaper of Death arrives at Bill's home in the body of the young man, explaining that Bill's impassioned speech has piqued his interest after an eternity of boredom. Given Bill's "competence, experience, and wisdom," Death tells Bill that in return for a few extra days of life, Bill shall be his guide on Earth. Bill agrees, and Death places himself at Bill's right hand as "Joe Black" and establishes a constant presence in Bill's home and work. Susan finds Joe appealing, but cannot understand why he is treating her like a stranger.
Bill's best efforts to navigate the next few days — knowing them now to be his last — fail to keep events from going rapidly out of his control. Drew is secretly conspiring with a man bidding for Parrish Communications, so he capitalizes on Bill's strange behavior to convince the board to vote him out as Chairman, using information given to him inadvertently by Bill's son-in-law Quince (Jeffrey Tambor) to push through approval for the merger which Bill had decided to oppose.
Susan falls deeply in love with Joe, who, now under the influence of human desires, becomes attracted to her as well. Bill angrily confronts him about it, but Death intends to take Susan with him for his own.
As his last birthday arrives, Bill makes a last attempt to demonstrate to Joe the meaning of true love and all it encompasses — especially honesty and sacrifice. Realizing finally that Susan was never in love with him, but rather the young man whose body he now uses, he abandons his plans to take her. He also comes to Bill's assistance in regaining control of his company, exposing Drew's underhanded business dealings to the board.
Informing her that he is leaving without saying why, Joe says a last goodbye to Susan. She senses the fact that he is more than he appears, and through an intense moment, she realizes who he really is, though she is unable or unwilling to vocalize this realization. Nonetheless, she is now aware of what is really going on between Joe and her father, and she dances with her father one last time, knowing he will be departing with Joe afterward. Bill takes the time to assure her that everything is alright, and that he has no regrets. As the fireworks go off at the end of the party, she tries to get Bill to go down and watch them with her, but he realizes it is time for him to go with Joe, and though he merely says "I'm just going to catch my breath." Susan knows that she won't see him again, so she gives him a final hug and walks down to watch the fireworks. Bill meets Joe at the top of a hill overlooking the party and together they reminisce about how difficult it is to let go of life. Joe escorts Bill away, with Susan observing from a distance. She then is astonished to see Joe return, only to discover that he is the young man whose body Death used, and this is his first glimpse of her since the coffee shop. Susan says, "I wish you could have known my father," knowing now that he is gone but that she is not alone.