William Pedersen was born in Stamford, Connecticut, in 1908. He received an undergraduate degree from Harvard College in 1931 and continued on to receive a Master of Architecture degree from the Harvard University Faculty of Architecture in 1934. Entering the job market in the midst of the Depression, Pedersen opted to set out on his own and started an architectural firm in Stamford, Connecticut. He kept the firm running until World War II, when he served in the military. After the war, he joined the firm Harrison & Abramowitz. During his time with the firm, he worked on the design for the Alcoa Building (1953) in Pittsburgh, Pennsylvania.
In 1952, Pedersen established a new firm with architect Paul Tilney. Tilney left the firm in 1964, and it was renamed William F. Pedersen & Associates. During the 1970s, Pedersen worked on urban renewal projects in New Haven, Connecticut. His firm's work also included a master plan for the American Museum of Natural History in New York City and the design of the ICI Building in Stamford, Connecticut. Although his firm won a competition for a memorial for Franklin D. Roosevelt that would have stood on the Washington Mall in Washington, D.C., the project was never completed due to financial issues. The firm had offices in Manhattan and New Haven and remained open until Pedersen's retirement in 1989.
Pedersen was a Fellow of the American Institute of Architects and was a member of the Century Association and the Harvard Club of New York.
William Pedersen died in 1990.