John Kasmin (b. 24 Sept 1934) is a British art dealer whose gallery promoted British and American Color field painting in the 1960s. He went to Magdalen College School in Oxford and then worked with the established London Art dealer Victor Musgrave. In 1960 Kasmin met David Hockney and when he set up his own gallery in 1963 Hockney became one of his first artists. (Kasmin appears, as himself, in the 1974 Hockney biopic, A Bigger Splash.) Other artists that Kasmin showed included: Barnett Newman, Ad Reinhardt, Frank Stella, Kenneth Noland, Morris Louis, Helen Frankenthaler, Anthony Caro, William G. Tucker, John Latham, Richard Smith, Bernard Cohen, Robin Denny, Howard Hodgkin and Gillian Ayres.
Kasmin opened a large white space on New Bond Street that was unusual for the time - until then most commercial galleries had been domestic in scale. Kasmin closed his gallery in 1972 but continued to operate in partnership with other London dealers into the 1990s. He has a son called Aaron who is a successful artist. Kasmin also has a son, Paul, who is an art dealer.
John Kasmin briefly lived in New Zealand in the mid-1950s, working temporarily as an orderly at Wellington Public Hospital. Many young colonial bohemians of the day were entertained by his quick acerbic wit.
Kasmin married Jane Nicholson niece of artist Ben Nicholson and had two children