In 1939, Porter was sent to Bucharest, Romania on an academic post with the British Council to teach English at the University of Bucharest.[2] In 1940 he was transferred to the Legation, and remained there until it was withdrawn from Romania on 12 February 1941.
On 1 March 1941, Porter was recruited by SOE,[4] and was one of a covert three-man mission that was parachuted into Romania in December 1943 to instigate resistance against the Nazis at "any cost" (Operation Autonomous). The SOE agents were captured and held as prisoners-of-war until, on 23 August 1944, King Michael of Romania carried out his anti-German coup d'état. Porter met King Michael that night and remained in the country during the King's desperate efforts to prevent Soviet domination. In June 2008 he was awarded the Cross of the Royal House of Romania.
Porter wrote two books after retirement: Operation Autonomous: With SOE in Wartime Romania (ISBN9780701131708) and Michael of Romania: The King and the Country (ISBN9780750938471). Operation Autonomous was short listed for the Time-Life/Pen Award for non-fiction. In 2005 he was made Commander of the Romanian order of "Meritul Cultural".[5]