Encouraged by his high school teachers there, he studied performing arts at the United States International University in San Diego before landing the role of Billy Crocker in Cole Porter's Anything Goes in London's West End.

Since his debut, he has played a number of roles in various musicals both in the West End and on Broadway, including Miss Saigon, The Phantom of the Opera, Sunset Boulevard, and Matador.

After appearing in Sam Mendes' production of The Fix, he was nominated for the 1998 Laurence Olivier Award for Best Actor in a Musical and, in the early 2000s, returned to the role of Billy Crocker in the revival of Anything Goes.

Before venturing into British television, he featured in the American television dramas Titans and Central Park West, but is better known for his acting and presenting work for the BBC; this includes his work for CBBC in its earlier years, his self-produced entertainment programme Tonight's the Night, and his BAFTA Cymru-nominated role of Captain Jack Harkness in the 2005 revival of the sci-fi series Doctor Who and its spin-off Torchwood.

[15] Barrowman's professional acting career began in London's West End in October 1989, playing the role of Billy Crocker in Cole Porter's Anything Goes at the Prince Edward Theatre, alongside Elaine Paige as Reno Sweeney and Bernard Cribbins as Moonface Martin.

A Celebration of Ira Gershwin at the Royal Albert Hall in 1996,[21] and he was nominated for an Olivier Award for Best Actor in a Musical in 1998 for originating the role of Cal Chandler in The Fix,[22] a performance he repeated in Cameron Mackintosh's 1998 gala concert Hey, Mr Producer!.

His only other Broadway credit is in the role of Barry in the Stephen Sondheim revue Putting It Together (1999–2000) at the Ethel Barrymore Theatre opposite Carol Burnett and George Hearn.

[24] On 23 March 2002, Barrowman took part in the 'Concert for Peace' along with 200 other performers in a gala show at Theatre Royal, Drury Lane, to express their opposition to the US-led war against Iraq.

That summer, Barrowman was on a Judges panel with Andrew Lloyd Webber, David Ian, and Zoë Tyler on BBC One's music talent show How Do You Solve a Problem like Maria?.

[41] He guested on the BBC Two comedy panel quiz show Never Mind the Buzzcocks (Series 19, Episode 5),[42] challenging host Simon Amstell to a "gay-off".

Barrowman first starred as Peter Fairchild in Central Park West (1995)[56] a show American film critic Ken Tucker calls "a tale of ritzy, ditsy New York City careerists—some struggling to make it, others plotting to retain their status and power.

"[57] Television critic David Hiltbrand called Barrowman's character a "Prince Charming ... a virtuous, hardworking assistant DA who keeps getting distracted by women who swoon in his path.

[61] Entertainment Weekly reported that Barrowman would appear in the 2010 season of Desperate Housewives, "for a minimum of five episodes, portraying Patrick Logan, the ex-boyfriend at the center of the Angie Bolen (Drea de Matteo) mystery.

By July 2016, he signed a deal that allows him to continue being a series regular on Arrow as well as the other superhero shows produced by Greg Berlanti, including The Flash and Legends of Tomorrow.

[72] On 4 February, despite being one of the favourites to win, Barrowman and Sharutenko faced Stefan Booth and his partner Kristina Lenko in the skate off and were eliminated by the judges' by a vote of 3 to 2.

Barrowman played recurring guest character Captain Jack Harkness, an omnisexual time traveller from the 51st century in the BBC science fiction drama Doctor Who when the series was revived in 2005.

Jack became so popular, he was given his own show – Torchwood, a Doctor Who spin-off series featuring a team of alien hunters based in modern-day Cardiff, which premiered in 2006.

American film and television critic Ken Tucker describes Barrowman's role on Torchwood as "dashing", "utterly fabulous", "celestially promiscuous", and "like Tom Cruise with suspenders, but minus the Scientology".

In the show, Jack "tracks down—and occasionally beds—ETs with the help of his quartet of bedazzled groupies—slash—Experts in Their Fields: One's a doctor, one's a cop, one's a scientist, and one... makes coffee and late nights piping hot.

[77] In 2008, Barrowman appeared in the two-part 2008 series finale, "The Stolen Earth"/"Journey's End" and reprised the role of Captain Jack Harkness in the "Doctor Who: Tonight's the Night" special.

Barrowman's first published work of original fiction was a Torchwood comic strip, titled Captain Jack and the Selkie, co-written with sister Carole.

Barrowman's début fantasy novel titled Hollow Earth, co-written with his sister Carole, was published in the United Kingdom on 2 February 2012, by Buster Books.

The novel is about twins Matt and Emily ("Em") Calder who share an ability that allows them to make artwork come to life, due to their powerful imaginations.

In 2018, John and Carole Barrowman teamed up with Legendary Comics and graphic novelist Erika Lewis to create Acursian, featuring a modern-day anti-hero dealing with Celtic mythology.

[97] Barrowman was one of 48 British celebrities who signed a public notice warning voters against Conservative Party policy towards the BBC prior to the 2010 general election.

[108] In mid-March 2017, Barrowman and Gill held a "big bad garage sale" in their Palm Springs home, in which they sold Doctor Who and Torchwood memorabilia.

[109][110] In February 2008, talking about Barrowman's on-set behaviour, Doctor Who co-star Freema Agyeman said in an interview to The London Paper newspaper, "John will walk about with his chap [penis] hanging out, having conversations with people.

[115] Julie Gardner, an executive producer on Doctor Who and Torchwood, confirmed that she received a complaint about Barrowman's on-set behaviour "around 2008", for which he was reprimanded at the time.

[116] On 7 May 2021, Barrowman issued a statement that read: My high-spirited behaviour which was only ever intended in good humour to entertain colleagues on set and back stage has been well-documented, including in my autobiographies and even in song.

Fifteen years ago was bawdy behaviour [...] the fact it was stories I've already told, haven't hidden anything [...] they've tried to turn them into sexual harassment which it absolutely is not.