While political editor of The Daily Mirror he was a close advisor of Neil Kinnock. After Tony Blair became leader of the opposition, Campbell left the newspaper to become his spokesman. After Blair became Prime Minister in 1997, Campbell became his chief press secretary and in charge of the government's press machine.
In June 2003 he was a central figure in the "dodgy dossier" controversy. He demanded an apology from the BBC over the claim that the British Government had "sexed up" a dossier about Iraqi weapons of mass destruction. The BBC has so far refused to apologise, sticking by their claim.