After studying mortgage banking at Northwestern University, Foster joined the family firm in 1946 as a salesman. In the '50s he took over the company's uptown residential-sales office; by 1967 he was president of the firm. Under his direction, Shannon & Luchs became'a full-service company dealing with sales, rentals, commercial property, mortgages, and construction.

Foster Shannon worked to make Washington a "full-service" city. He led the fight for urban redevelopment and for construction of the DC Convention Center; he pushed for the expansion of Dulles Airport and spearheaded efforts to promote the Washington-Baltimore region. He never lost his faith in real estate or his home town. During the business exodus to the suburbs that followed the 1968 riots, Shannon refused to move his company's headquarters out of DC. "This is where we started, and this is where we'll stay," he said.

When he died of cancer in 1989, a friend remembered Foster Shannon as "one in a passing breed of Washington-based people deep into a family business but also with a wide range of interests, a solid perspective on issues, and the ability to relieve tensions with a sharp sense of humor. And he made it look easy."