Aged 38, Purnell is the fastest-rising star in the Labour firmament. He spent four years as an adviser to Tony Blair before becoming an MP in 2001. A former Islington councillor, he entered the cabinet in June 2007 as culture secretary and was made work and pensions secretary earlier this year.
What is his background?
The son of an accountant and a teacher, Purnell studied philosophy, politics and economics at Oxford while working as a researcher for Blair. After a spell as a researcher at the Institute for Public Policy Research, he worked for the BBC, rising to be head of corporate planning.
Where does he sit politically?
Purnell is thought to be a member of the 'Primrose Hill set', with David Miliband, Liam Byrne and Jim Murphy. It is said they broadly share Blair's world view. Purnell's welfare reform green paper was this week attacked by left-of-centre critics.
Why he is a man to watch
As pensions secretary, Purnell has one of the biggest jobs in government. The Spectator's Fraser Nelson has declared Purnell the best candidate to succeed Gordon Brown, saying 'he has the gift of sounding like an ordinary human being'.
Something you might not know
In January 2007, the Daily Mail reported Purnell was given an 'easy ride' on the BBC's Newsnight due to a relationship with one of the producers, Thea Rogers.