Toumanoff's parents fled the October Revolution in St. Petersburg in 1917. His father joined the White Russian forces during the Russian Civil War, while his mother was put to death by the Bolsheviks. Cyril Toumanoff was initially sheltered by his maternal grandparents in Astrakhan. In 1928, Toumanoff's father was able to escape to the United States, bringing his son with him. Cyril Toumanoff attended the Lennox School which he graduated from in 1931 and went to Harvard. His educators John Coddington and Robert P. Blake helped him secure funding for travel to Brussels to study Armenology under Nicholas Adontz and then to Berlin, where he studied Georgian under Michael Tsereteli. During these years, Toumanoff converted to Roman Catholicism. A breach with his Orthodox Christian father ensued and was only terminated when the two reconciled at the latter's deathbed in 1943.