Leontiev was born and grew up on his father's estate. His father, a nobleman, was a military officer but was discharged for "riotous behaviour". Still, the intervention of the Russian empress in behalf of the Leontiev brothers made him able to enter the Imperial Corps of Pages. He was engaged at 23 but broke off the relationship for the sake of "freedom and art"" a decision that made things difficult for him. After completing medical school in Moscow, Leontiev saw service as a doctor during the Crimean War.