text: The Londoner beat competition from the likes of Florence + The Machine, Wolf Alice and Supergrass star Gaz Coombes.
  "I don't know what to say," the 26-year-old said as he accepted the prize, then invited all the other nominees to take to the stage with him.
  He then broke down in tears as he dedicated his award to the victims of the Paris terror attacks.
  The musician spent his early 20s living in the city, and busked on the metro as a struggling musician.
  He told BBC News he had returned to Paris last weekend to support friends who had been caught up in the tragedy.
  Reflecting on the Mercury Prize, he said: "I always believed in my music but after Paris happened, I was very down.
  "I didn't think I would win. I always wanted to be nominated for this award, but I didn't think to myself that I'd win it. I always made a joke about it!"
  The musician's debut album is a searingly-personal collection of piano-based songs, which critics have called "bold", "brilliant" and "astonishing".
  It touches on his turbulent upbringing in Edmonton, London, as well as the three years he spent sleeping rough in Paris.
  "I made this album thinking only about 50 people would listen to it," he told the BBC. "My music isn't mainstream music.
  "It goes to show that you've just got to be sincere in your work and people will listen to it."
  The Mercury Prize recognises innovative albums produced in the UK and Ireland. Former winners include Pulp, Primal Scream and PJ Harvey.
  The competition for this year's title was particularly fierce, with presenter Lauren Laverne calling the judges' decision "impossible".
  "They all had an equal chance," she said of the nominees.
  "But that's what's nice about the Mercury. It's not something where your big artists come in and scoop up all the gongs. It could be anybody's."
  A panel of 12 musicians, broadcasters and music writers selected the winner, casting their final votes on the night of the award ceremony.
  The jury included former nominee Corinne Bailey Rae, who said the decision came "really close to the wire".
  The judges began their deliberations with a longlist of 298 albums earlier this year, which was whittled down to a shortlist of 12, announced in October.
  They were:
  Read more on the shortlisted acts
  Newcomer Eska, whose self-titled album is an unusual combination of soul, psychedelia and jazz, said there were "12 winners" on the night, with newcomers and established artists sharing the limelight equally.
  "There's no winning to be had, apart from a pocket full of money," she added. "A very big pocket full of money!"
  Scottish composer C Duncan agreed that simply being shortlisted had changed his career.
  "It was one of those albums that completely slipped under the radar," he said of his debut record, Architect. "But since it was nominated for the Mercury, so many more people have listened to it and discovered it, which is nice."
target: Benjamin Clementine has won the 2015 Mercury music prize for his debut album, At Least For Now.