The 60-year-old writer took the £50,000 prize for a second time with Bring Up The Bodies a tale of Tudor treachery that follows the fates of Henry VIII's right-hand man, Thomas Cromwell, and the monarch's second wife, Anne Boleyn.
It is the second book in a planned trilogy and a sequel to Wolf Hall for which Mantel won the Booker in 2009.
In receiving the award at a glittering dinner ceremony at London's medieval Guildhall last night, she beamed: "Well I don't know, you wait 20 years for a Booker Prize and two come along at once. I regard this as an act of faith and a vote of confidence."
Mantel, who now joins Peter Carey of Australia and JM Coetzee of South Africa as double winners, added: "I have to do something very difficult now.
"I have to go away and write the third part of the trilogy. I assure you I have no expectations that I shall be standing here again."
Sir Peter Stothard, who chaired the judging panel, said the book, "utterly surpassed" the first volume. He said: "She uses her art, her power of prose, to create moral ambiguity and the real uncertainty of political life, political life then and the pale imitation of political life now".
He said the book, which concentrates on the end of Henry VIII's marriage to Anne Boleyn, had made "one of the best-known pieces of English history" come alive again "as though for the first time".
Sir Peter compared the work to that of novelist DH Lawrence and likened Cromwell to the main character in Mario Puzo's Godfather books.