Brook was born to Russian immigrant parents. At the age of twelve, when recovering from a bout with infantile paralysis, he began to paint under the tutelage of a portrait painter who lived in his neighborhood. He began formal study at Pratt Institute in New York, but quickly changed to the Art Students League where he studied under Kenneth Hayes Miller from 1914 into 1919. The following year he and the artist Peggy Bacon who had also been at the League, were married.
From 1924 to 1927 Brook worked as assistant director of the Whitney Studio Club under Juliana Force. Substantial recognition of his work began in the late 1920s. In 1930 his painting Interior won second prize at the Carnegie Institute, Pittsburgh, International exhibition; the Carnegie presented a one-man exhibition of his work in 1934. A Guggenheim Fellowship awarded him in 1931, enabled him to travel to Europe. From 1933 to 1936 Brook was teaching at the Art Students League; he again taught there again, 1942-43. Like so many other artists active in the period of the Great Depression, Brook worked in mural art, producing in 1939, Writing the Family Letter and Reading the Family Letter for the United States Post Office Department building in Washington, D. C.
Brook's early works tended to be ethereal and classically inspired, akin to the early work of his teacher, Kenneth Hayes Miller. But as his work developed he came to focus on the realities of the contemporary urban scene. With Miller, Isabel Bishop and others, he was considered a part of the "Fourteenth Street School" of figurative painters.
Brook did not begin to exhibit in Academy annual exhibitions until the late 1940s, but for twenty years thereafter he was a consistent participant. The Academy awarded him the Saltus Medal in 1950, Carnegie Prize in 1953, Altman prizes in 1957 and 1960, and the Proctor prize in 1964.
