The show was created by John Sacret Young and William Broyles, Jr. and focused on combat medics in the Vietnam War.

In 1992, Wells co-wrote the teleplay of The Nightman, helping to adapt it into a television film from the radio drama by Lucille Fletcher.

He also wrote the screenplay for Entertaining Angels: The Dorothy Day Story; that project was produced in 1996 and starred Martin Sheen and Moira Kelly.

In 1994, Wells executive-produced the pilot of the NBC medical drama ER, created by novelist Michael Crichton.

ER marked the start of Wells longstanding collaboration with producer/director Christopher Chulack and music composer Martin Davich.

Wells and Crichton also received an honorable mention at the Wise Owl Awards in the Television and Theatrical Film Fiction category.

Wells was also nominated for a Humanitas Prize (in the 60-minute category) and an Emmy Award for Outstanding Writing for a Drama Series for the episode "The Healers".

[8] Wells and the producers were nominated for the Emmy Award for Outstanding Drama Series at the 1998 ceremony for their work on the fourth season.

Wells stood down as show runner after the fifth season but remained an executive producer and major creative force behind the series.

He returned as a writer for the fifteenth and final season and wrote and directed the episode "Old Times" which featured several past starring cast members including Noah Wyle, George Clooney, Julianna Margulies, and Eriq La Salle.

Wells served as an executive producer and writer for the series but it was cancelled after only nine episodes due to low ratings.

Wells worked as show runner on Third Watch for its first three seasons and served as an executive producer throughout its six-season run.

[22] Wells wrote four second-season episodes the premiere entitled "The Lost",[23] "Faith",[24] "Requiem for a Bantamweight",[25] and the finale "...and Zeus Wept".

[27] Wells wrote a further four episodes for the third season in 2001 – "September Tenth",[28] "After Time",[29] "Adam 55-3",[30] and "Two Hundred and Thirty-Three Days".

[31] Bernero took over as show runner after the third season and Wells remained attached as an executive producer until Third Watch ended in 2005 but did not write any more episodes.

[34] Starring William H. Macy as an alcoholic single father of six children, Shameless was the best performing first-year drama in Showtime's history.

Other projects from Wells include the unsold pilots to Bad Girls on NBC, Prodigy Bully for Fox and The Deep Mad Dark for TNT, American Woman for Paramount Network and the miniseries Maid for Netflix.

In June 2019, Wells signed an overall deal to stay at Warner Bros. Television with two more shows in the works: Heart of a Lion from Showtime and My Ex-Life for Apple TV+.

[36] Wells is currently working on a pair of dramas from Warner Bros. Television: Ke Nui Road and the anthology series take on the book Things That Make White People Uncomfortable for HBO Max.

In April 2023, MGM+ ordered ten episodes of the series The Emperor of Ocean Park based on Stephen L. Carter's best-selling novel of the same name, with Sherman Payne as the writer and Damian Marcano set to direct.

Wells serves as an executive producer on the medical drama series The Pitt for the streaming service Max.

Wells made his directorial debut with the film drama The Company Men, starring Ben Affleck.

This displays the kind of guts he always brought to his television work, which one can only hope continues on in other future film projects.

"[41] His second film, August: Osage County (2013), which he directed from a script by Tracy Letts, stars Meryl Streep, Julia Roberts, and Ewan McGregor.

[42] Sienna Miller co-starred,[43] along with Omar Sy, Emma Thompson, Daniel Brühl, Alicia Vikander, and Lily James.

John Wells Productions won a Peabody Award in 1999[45] and 2000[46] for The West Wing and again in 2001 for Third Watch's '"In Their Own Words," which told the stories of real-life responders to the 9/11 attack on New York City.

On May 18, 2014, Wells received an honorary Doctor of Fine Arts degree from Carnegie Mellon University, where he graduated from in 1979.