On April 29, 1967, Brewster married Anne Moen Bullitt Biddle (1924–2007) at Glyndon, Maryland. She was the daughter of journalist Louise Bryant and William C. Bullitt from their marriage in 1923. Bryant, her mother, was the widow of John Reed, who wrote "Ten Days That Shook the World" while living in Moscow through the Bolshevik revolution; while Bullitt, her father, served as ambassador to the Soviet Union and France under President Franklin D. Roosevelt. Anne Biddle was previously married to Caspar Wistar Barton Townsend, Jr., Nicholas Duke Biddle and Roderic More O'Ferrall. This, Brewster's second marriage, ended in 1969.