Mark Bennett: Downing Street insider who went on to lead a local authority and spearhead life-enhancing projects

The sudden death of Mark Bennett from a heart attack at the age of 44 has robbed both local government and the gay movement of a high profile campaigner. But it was as a junior civil servant that he came closest to the centre of power. In 1997, he went to work at 10 Downing Street, the only man in the famous garden room staffed by women who normally acted as administrative and secretarial support to the prime minister of the day. Tony Blair, with whom he worked closely during those early days at No 10, said: "He was intelligent, immensely hard-working and above all, a warm and generous spirit who was a pleasure to be around."

Bennett moved over to work for Alastair Campbell, then Blair's media chief, acting as "gatekeeper", support staff, and importantly for Campbell, friend. He was never scared of commenting or giving opinions on what Campbell's writing or actions. He once gave Blair a slow hand cap for a speech that he didn't think was very good; his own jokes, if rejected by Blair, were scooped up by John Prescott.

In 2001, he resigned from his civil service career so that he could support Labour at the general election, becoming Campbell's right-hand man for its duration. He would continue to offer support and help to Campbell when he quit No 10, playing a vital role in helping him to put together his memoirs of the Blair years. He was also on hand when Campbell gave evidence to the Chilcot inquiry into the war on Iraq, helping him to prepare his evidence and reading through all the background papers to prepare for the onslaught of media inquiries.

Alastair Campbell recalled someone who was very important to him: 'He was a huge part of my life. He was very political, something we hadn't realised at first as he was in the civil service. He was a very committed team player, with a very funny dry sense of humour. He was always looking to do something more. He had wanted to be an MP and a screenwriter. Sadly he was thwarted in both."

Bennett had graduated in television and film studies from Staffordshire University between two bouts of studying at the Civil Service College, from where he had been recruited to No 10. He was to continue to write scripts, film reviews and articles for the rest of his life. He was writing a political history of Lambeth in south London when he died.

On leaving the service, he went to work for Siobhain McDonagh, MP for Mitcham and Morden. "He was a great writer," she remembered. "He wrote one of the best lines in a speech for me: 'Dogma never delivered a baby.'" He was also a great singer of light opera, founding a Gilbert and Sullivan society. On the surface he seemed quiet, but there was so much behind that. He was so many things on so many levels. He could be flamboyant and he was a great party animal. He loved dancing.

Bennett was a moving force in initiating a campaign to get digital hearing aids introduced. One of his two sisters was profoundly deaf, and working together with the RNID, he and McDonagh fought to establish the system's widespread use, and to destigmatise deafness.

In 2003, he moved on to working for the GMB union on its campaigns, then for the Labour Party. He failed to be selected for a parliamentary seat; but in 2005 was elected to Lambeth Council, serving for several years as a cabinet member responsible for several portfolios. "I had entered politics," he said simply, "to help people."

He became Mayor of Lambeth in 2013, throwing himself into the role, showing enthusiasm for everything that he was asked to do. Duties ranged from welcoming the Queen and the Duke of Edinburgh to the National Theatre, to launching a new Scout and Guide unit at the Evelina London Children's Hospital. Particularly close to his heart was the support he gave to The Trussell Trust which runs food banks across London.

His love of history was often reflected in speeches and articles, as was his exuberance as shown in his description of this year's London New Year's Parade: "Giving out oranges, rain dampened robes but not spirits."

Bennett was also a member of the Labour Campaign for Lesbian and Gay Rights; in 2013 he took part in the London Gay Pride Parade wearing his mayoral chains. In November, he took part in a Reclaim Vauxhall walk along the Albert Embankment in south London, the week after a homophobic attack. He was particularly proud and touched to have received a letter from the lesbian and gay rights movement praising him for being a "fantastic LGBT role model in our community".

He owned a dog, Index; welfare of animals was also very important to him, and he sat on the board of the Greek Animal Welfare Fund. Bennett was born and brought up in Berkshire, his parents running the local pub in Crowthorne where he went to the local school. He believed strongly that people should be judged for what they did "at the time and not on their past".

Mark Bennett, politician and campaigner: born Crowthorne, Berkshire 9 July 1969; died London 6 February 2014.