In 1940, Bain joined a joint venture with J. Lister Holmes, William Aitken, George W. Stoddard, and John T. Jacobson to design Yesler Terrace, Seattle's first public housing project.
During World War II Bain served as camouflage director for the state of Washington.
He also joined other architects in joint-venture firms to design housing for war workers as well as other war-related projects.
The joint venture formed in 1943, with Floyd Naramore, Clifton Brady, and Perry Johanson was particularly successful, and became the basis for the post-war firm Naramore, Bain, Brady and Johanson (occasionally called "the combine"), predecessor to today's NBBJ.
Bain served as president of the Washington State Chapter American Institute of Architects (predecessor to today's AIA Seattle) from 1941 to 1943.