After World War II, Mavros became involved in politics and was first elected MP in 1946. He participated in several governments as Minister of Justice, Education, Trade and Industry, Economy and National Defence.
After the the Turkish invasion of Cyprus which led to the collapse of the military Junta in July 1974, Mavros became Foreign Minister in the national unity government of Constantine Karamanlis. In that capacity, he negotiated in Geneva, with his Turkish counterpart, the political status of Cyprus. The negotiations collapsed in August 1974 and the second phase of the invasion (Attila II) took place. In the first post-junta elections of 1974, Mavros led the revived Centre Union party (Centre Union - New Forces) which lost to Karamanlis' New Democracy.