In 1938, the marriage broke down, caused by Nicholson's relationship with Barbara Hepworth (May 20^th) to whom he was married for thirteen years (1938 – 1951). Nicholson had first travelled to St. Ives in 1928 where he met Alfred Wallis (August 29^th). In 1939 Nicholson and Hepworth moved to St. Ives where they established the St. Ives School of Art and their studios, also becoming members of the Seven and Five Society of St. Ives artists and sculptors.  Inspired by the work of his father, Sir William Nicholson, and by Picasso, Nicholson painted geometric shapes. 

His work was considered by many to be outrageous and, until the late 1940s, he struggled to make a living. In the 1950s, however, he began to win international prizes including the Carnegie Prize (1952) and was exhibiting worldwide.  By the time of his death he was regarded by many as Britain's greatest living artist, as indicated by the award of the Order of Merit (OM), in 1968.    

Following his divorce from Hepworth, he lived in Switzerland with the photographer Felicitas Vogler to whom he was married for twenty years.