For many years he taught a popular course at Harvard known informally to his students as "Brunch with Brinton". Brinton was known for his witty, convivial, and urbane writing and commentary, and was fluent in French. During World War II he was for a time Chief of Research and Analysis in London in the Office of Strategic Services. He was also Fire Marshal for St. Paul's Cathedral in London, which withstood the Blitz with minor damages. After the war, he was commended by the United States Army for "Conspicuous Contribution to the Liberation of France" and was chairman of the Harvard Society of Fellows in the late 1940s. Membership during that period included McGeorge Bundy and Ray Cline, who would go on to become quite influential in national security and intelligence.
In the early 1960s Brinton was the dissertation supervisor at Harvard of the young historian Will Johnston. He also served as an advisor for historian Elizabeth Eisenstein, author of ''The Printing Press as an Agent of Change''.
On February 19, 1968, Brinton testified at the Fulbright Hearings on the Vietnam war as to the nature of the Vietnamese opposition, saying that Americans are sympathetic to a revolution but not a Communist one, and that if Ho Chi Minh had not been a Communist, "The whole story would have been different."
