Coulombe started his career at Rexall, a chain of American drugstores. In 1958, he was asked to test the launch of Pronto Markets, a store brand to compete against 7-Eleven. After running six Pronto Markets in the Los Angeles area, Rexall asked Coulombe to liquidate them; he decided to buy them out instead. In 1967, Coulombe changed the name Pronto Markets to Trader Joe's. He led the chain to success and sold it in 1979 to German billionaire Theo Albrecht, co-founder of the Aldi supermarket chain. Coulombe continued with Trader Joe's as chief executive officer until retiring in 1988.
In 1952, Coulombe married Alice Steere, whom he met at a party while they were students at Stanford. Alice served on the board and is a life trustee of the Los Angeles Opera. They had three children, Joe, Charlotte, and Madeleine. Coulombe and his family lived in Pasadena, California.