Ambrose was signed by the Montreal Alouettes in 1950 after his performance as a junior football player attracted attention. In addition to his role as a tackle, Ambrose occasionally acted as a placekicker for the Alouettes. A forum of quarterbacks named Ambrose the most likely to win the rookie of the year award in November due to his status as "about the only one of the slim rookie crop to see much action". The Alouettes re-signed Ambrose in July 1952.