He joined the Royal Canadian Air Force in 1935 and during World World War II he commanded a Canadian fighter sector in continental Europe. In the early 1950s, he was a senior staff officer at the Headquarters of Canada"s Air Defence Command in Saint-Hubert, Quebec before being appointed to further staff duties at Number. 4 ATAF at Lansberg in Germany.
In September 1958 MacBrien took over as Air Officer Commanding Air Defence Command.
Deputy commander in chief at the Supreme Headquarters Allied Powers in Europe Headquarters in Belgium in 1967. From August 1967 to January 1969 MacBrien was the Deputy Commander of North American Aerospace Defense Command (North America Air Defense).
MacBrien died in 1986. His body was buried in the Beechwood National Military Cemetery in Ottawa.