Rowntree had played in bands with Graham Coxon while the two were growing up in Colchester, and knew Coxon’s father who taught jazz classes at Landermere. In 1989, Coxon introduced Rowntree to Damon Albarn, who was forming a band around Goldsmiths, University of London. Rowntree was asked to join, and left his job to move to London. With the addition of Alex James, and after many name changes, the band settled on Blur and were signed to Food Records, which was distributed through EMI. EMI later acquired Food Records and Blur were absorbed into EMI.

In the early 1990s, Rowntree was a heavy drinker; he stopped drinking alcohol in 1993 after a particularly heavy drinking session with members of the band Siouxsie and the Banshees. However, several years later, he began a cocaine habit. This led to a public incident in 2003 when, during a TV interview of Blur for MuchMusic by Canadian journalist Nardwuar the Human Serviette, Rowntree was seen mocking and physically intimidating Nardwuar throughout the interview. Rowntree has apologised several times since for his behaviour, saying that “the day after a cocaine binge I’d sometimes fly into a murderous rage,” and that this was the case on that day. By 2007, he stated that he had stopped using drugs and was “active in the recovery community”. He has also said that he keeps a clip of the interview on his phone, to watch if he ever considers relapsing into drug use.

In 1994, Rowntree married Paola, a Canadian woman. The couple divorced in the early 2000s. In 2007, he was dating Michelle de Vries.

Rowntree obtained a full pilot’s licence in 1995. Rowntree also holds a foundation licence for amateur radio in the UK since 2012 using the callsign M6DRQ. He upgraded his licence in 2016 to advanced with the new call sign 2E0DVR.

Rowntree has been a keen activist and supporter of the Labour Party since becoming a member in 2002, and has been chairman of London’s West End branch. In April 2007 he unsuccessfully contested the safe Conservative seat of Marylebone High Street on Westminster City Council. In July 2008, he fought the Labour-held seat of Church Street, a Labour stronghold since its creation in the 1960s, but a swing from Labour to the Conservatives of 14.1% meant that he was again unsuccessful, as the Conservatives gained the seat.

Rowntree is a computer animator, and owns an animation company called Nanomation. He directed two series of the South Park-esque animated show Empire Square, which made its TV debut on Channel 4 on 18 February 2005. He is also interested in computer graphics and has contributed to three research papers on topics related to non-photorealistic rendering.

Rowntree trained to become a solicitor when Blur took a hiatus in 2006. He is employed in the criminal department of Kingsley Napley, a firm of solicitors based in Farringdon, central London.

Rowntree supported the 2003 invasion of Iraq and in 2007 said, “I’m not a pacifist, I do believe that some things are worth fighting for, and dying for. I understand that that’s easier to say, I’m not being the one who’s asked to die, but Saddam was such an illegal ruthless bastard I didn’t shed any tears for it [the war].”

In February 2008, he was selected by the Cities of London and Westminster Constituency Labour Party to stand against Conservative MP Mark Field at the 2010 General Election. He was defeated at that election. In 2011, Rowntree sought selection as Labour candidate for Norwich South; he lost to Clive Lewis, a journalist and former soldier, who went on to be elected as MP.

In August 2014, Rowntree was one of 200 public figures who were signatories to a letter to The Guardian opposing Scottish independence in the run-up to September’s referendum on that issue.

In the Norfolk County Council election on 4 May 2017, he was elected as county councillor for the University division in Norwich.

On 31 July 2018, Rowntree appeared in the video for Slaves’ newly-released single, “Chokehold”, as a drummer auditioning for a part in the band.