Jack was born in January, 1969, and was raised by his mother Judith (Veronica Cartwright) and stepfather Daniel (Beau Bridges). His mother did not know he was gay ("How could she not know? What is she, headless?" Karen demanded), and his stepfather was not close to him. He claims to have come out as early as preschool. While he was in high school, Jack befriended college student Will Truman (Eric McCormack) and helped Will realize his own homosexuality. They have been best friends ever since.

When the series begins, Jack's home is unknown but he is living with Will while his floors are re-done. At the start of season three however, Karen refers to him as having been living 'above a blinking light in Times Square'. At the end of season one, Jack agrees to marry Karen's maid Rosario (Shelley Morrison) in order to secure her green card. Jack lives with Karen for the entirety of season two but after a year together, the marriage is annulled when Rosario wants to date Karen's gardener. Therefore at the end of season two, Jack is homeless and moving in with Will, but when Will takes in his other best friend Grace Adler (Debra Messing) after an attempted burglary at her apartment, Jack agrees to sublet Grace's apartment — although Will, Karen, and his mother pay the rent. (In "Moveable Feast Part 1," it emerged that each of the three pays one half of the cost, meaning that Jack is actually collecting one and a half times the actual amount of his rent.)

Since the first season, Jack has established a close bond with alcoholic socialite

Karen Walker (Megan Mullally), who chooses to work merely as a source of distraction.

In season three, Jack undertakes a search for his real father, which ends when he discovers that his father died. Jack does, however, meet Elliot (Michael Angarano), his own biological son, whom he fathered by depositing at a sperm bank as a teenager so that he could buy a coat. He later discovers that the boy's mother Bonnie (Rosie O'Donnell) is a lesbian; she was a nurse at the sperm bank who stole Jack's deposit and was inseminated with it.

Jack's most consistent vocation results from his taking over the class of his acting teacher Zandra (Eileen Brennan) after she is fed up with his lack of talent. After taking everyone's money and leaving, another student(played by Stacy Keach) takes over the class and begins teaching the "McFarland method" ("acting is attracting") without Jack's knowledge. He trains to be a student nurse, but ultimately gives it up when, during Karen's fourth wedding, he meets Jennifer Lopez and becomes her back-up dancer (and, for a short time, Janet Jackson's back-up dancer), a career that fizzles as well.

In the seventh season, Jack embarks on a proper career as a producer on OutTV, a new gay television network. By season's end, his profile rises to the point that he is given a talk show of his own to host.

In season eight, Jack loses his job at the network after he speaks out against the new right-wing ownership of the show, which has given him a supposedly conservative cohost named Amber Louise (played by Britney Spears) who is actually a drug-taking, leather-loving lesbian. Shortly after this, he auditions for a role on a television show and - going against his natural over-dramatic acting style - he ends up getting the lead role of Chuck Rafferty, a straight alcoholic cop.

In the show's series finale, Jack had a brief and unwanted relationship with Karen's friend/rival Beverly Leslie, who left Jack as his sole heir in the case of his death. Beverly Leslie soon died when he was lifted off his penthouse balcony on a gust of wind, and Jack was left with millions of dollars. He is then shown to have lived with Karen (who had lost her money when she found out everything Stan owned was borrowed) and Rosario in his own mansion for the rest of his life after the show ended.