There he met and became close friends with Jackson Pollock, Philip Guston (formerly Phillip Goldstein), and Reuben Kadish.

He also became interested in the Post-Surrealist movement in Los Angeles and studied under Lorser Feitelson and Helen Lundeberg[3] In 1932, Lehman became an apprentice to David Alfaro Siqueiros, the Mexican muralist who was in Los Angeles working on a number of projects, including the first large-scale our door mural in the United States, Tropical America," ("La América Tropical".)

Lehman joined his group, Block of Painters, working on fresco murals portraying the discrimination and mistreatment of African Americans.

[5] In 1941, he was chosen by the Section of Fine Arts under the US Treasury Department to design a mural for a post office in Renovo, Pennsylvania, "Locomotive Repair Operation"[6] Moving to Woodstock, NY, in 1941, Lehman became part of the local Woodstock art scene and became good friends with Hervey White, a neighbor that lived down the road.

In 1946, Lehman returned to New York and taught art at his studio[3] and in 1950 married one of his students, Leona Koutras, with whom he had two children.

[10] In 1995 his work was included in the exhibition Pacific Dreams: Currents of Surrealism and Fantasy in California Art, 1934-1957 at the Hammer Museum.