It marks the end of a long and painful series of discussions to agree a deal, which prompted the resignation of his British agent, Pat Kavanagh, raised hackles in the literary world, and was described by novelist AS Byatt as folie de grandeur.
Last night HarperCollins refused to say how much they had agreed to pay Amis for his next novel, The Information, due out in May, and a book of short stories yet to be written.
But it seems likely that Amis, his American agent Andrew Wylie, and Malcolm Edwards, HarperCollins' publishing director, agreed a sum in the region of £480,000. Mr Edwards would only say: "We expect it to be a profitable deal."
Amis appears to have had the idea he was worth far more than he was getting from his then publishers, Cape and Penguin, in October, when his father, Sir Kingsley, was signed to HarperCollins for a two-book deal reputed to be worth £300,000.
Last night Amis and Mr Wylie went out to dinner to celebrate. Other publishers now await a deluge of similar demands from dissatisfied authors.