A native of Italy, Lebrun studied at the Naples Academy of Beaux Arts before emigrating to New York in 1925. He returned to Italy during 1932-33 where he furthered his studies in fresco before returning to the US where he executed a mural for the New York City Post Office. In 1936, 1938 and 1962 he was awarded the Guggenheim fellowship. During this time, he taught at the Art Student's League of New York.

In 1938, the artist relocated to California where he was active in Santa Barbara and instructed at Walt Disney Studios as well as at the Chouinard Art Institute in Los Angeles. Lebrun taught at the Broadmoor Academy/Colorado Springs Fine Arts Center in 1945 and at the Jepson Art Institute during 1947-50.

In 1952 Lebrun relocated to Mexico where he instructed at the Instituto Allende. He later taught at the University of California and at Yale University as a Visiting Professor.