The son of a missionary who was also a distinguished linguist,he has Russian blood on his mother's side, and was brought up in various locations including Jerusalem and Oxford. He studied politics at Magdalene College, Cambridge, and made a name for himself in student comedy revues, with the result that, after graduation, he starred with Alan Bennett in a series of sketch shows on BBC.
He progressed via newspaper, radio and television journalism to become one of the BBC's top political correspondents, and subsequently moved to ITN to take on a leading role there. One of his most memorable moments was when he waited outside the British embassy in Paris for Margaret Thatcher, in the hope of hearing her reaction to the first ballot in the party leadership contest of 1990, only to be pushed aside by her press secretary when she emerged from the building.
Sergeant's impressive appearances on programmes such as Have I Got News For You have made him, once more, a sought-after participant in television comedy and satire shows.