After graduating from Yale in 1936, Alsop moved to New York City, where he worked as an editor for the publishing house of Doubleday, Doran.
A month after the wedding, Alsop was allowed to transfer to the US Army, and he was immediately sent on a mission planned by the Office of Strategic Services (OSS).
From 1945 to 1958, Stewart Alsop was co-writer, with his brother Joseph, of the thrice-weekly "Matter of Fact" column for the New York Herald Tribune.
He published several books, including a "sort of memoir" of his battle with an unusual form of leukemia, Stay of Execution.
On June 20, 1944, Alsop married Patricia Barnard "Tish" Hankey (1926-2012), whom he met while training in England, where she lived.