John Richardson, the British-born art historian and curator who devoted more than a quarter century to writing a monumental four-volume biography of Pablo Picasso, died on Tuesday at his home in Manhattan while still at work on the final installment. He was 95.

His death was confirmed by Shelley Wanger, his editor at Alfred A. Knopf.

In a seven-decade career, Mr. Richardson wore about as many hats in the art world as anyone could. Along with being a historian and curator, he was at various times an artist himself, a dealer, an industrial designer, an auction-house executive and a collector.

Self-taught but possessing an unfailing eye and impeccable taste, he could spot a misattributed painting at an auction or zero in on the only gem among piles of junk at a flea market.

He also collected a wide circle of friends, including artists — Picasso, Georges Braque, Francis Bacon, Lucian Freud, Andy Warhol — as well as writers: Jean Cocteau, W. H. Auden, Nancy Mitford and Tennessee Williams. A celebrated raconteur, he was described by W magazine as “the man all New York wants to sit beside at dinner.”