Harris was educated at Ladycross School, a former preparatory boarding independent school in the coastal town of Seaford in East Sussex, as were his brothers Jamie and Damian. He says, "They were famous for discipline, with cold showers every morning", and that "You were never known by your first name there. You were either called by your number, or your last name. Since there were three of us, Damian was 'Harris Ma' for major. I was 'Harris Mi' for minor, and Jamie was 'Harris Minimus,' being the youngest and the smallest".[5] He then attended Downside School, a Catholic boarding independent school in the village of Stratton-on-the-Fosse (near the market town of Shepton Mallet) in Somerset, in South West England.[5] He went on to Duke University in the U.S., graduating in 1984 with a BFA in drama, then returned to England to train as an actor at the Central School of Speech and Drama, graduating in 1989.[6]
He gained widespread fame for his portrayal of Lane Pryce in the AMC period drama series Mad Men from 2009 until 2012. The show focuses on the lives of Ad Men in New York City during the 1960s. He first appeared in season three where he arrives as a British newcomer to Sterling Cooper, and later becomes a partner of the new agency SterlingCooperDraperPryce. Paul MacInnes of The Guardian wrote of Lane Pryce, "For much of his three season tenure on the show, Lane has seemed like the archetypal Englishman...He was polite, courteous, dry-witted, stingy. He was also apparently logical and keenly stoic, keeping calm and carrying on when Sterling Cooper broke up and its successor nearly went under."[7] Harris received critical acclaim for his final appearance in the episode "Commissions and Fees" as well as a nomination for the Primetime Emmy Award for Outstanding Supporting Actor in a Drama Series, losing to Aaron Paul for Breaking Bad in 2012. He returned to the series to direct the 11th episode of season 7, which aired in 2015.
He portrayed Captain Francis Crozier in the 2018 series The Terror, based on the Dan Simmonsnovel of the same name that provided a fictional account of the fate of Franklin's lost expedition. In November 2018, Harris was one of the first recipients of the Royal Canadian Geographical Society's Louie Kamookak Medal, awarded "for making Canada's geography better known to Canadians and to the world", for his portrayal of Captain Crozier. Harris said that he was "gratified" that the series inspired curiosity about the real expedition, remarking, "It’s sort of fitting that history will recall that it was the RCGS that first recognized The Terror, and that we as the recipients walked in the footsteps of Louie Kamookak."[10]
In March 2019, Harris joined Jared Leto in Sony's Spider-Man spinoff Morbius.[12] He plays the developer of psychohistory Hari Seldon in the Foundation television series produced for Apple TV+ which premiered in September 2021.[13] In March 2021, Harris was announced to have joined the cast of the biographical drama film Rothko, directed by Sam Taylor-Johnson.[14]
Harris married Jacqueline Goldenberg in 1989 and they divorced three years later.[16] On 16 July 2005, Harris married actress Emilia Fox,[17] the daughter of actors Edward Fox and Joanna David, and filed for divorce in January 2009;[18] the divorce was finalised in June 2010.
In April 2009, Harris met Allegra Riggio, a lighting designer and television host,[19] at a comedy club where a mutual friend was performing.[19][20] They married on 9 November 2013.[21] Harris resides in Los Angeles.[6]