Troyat was born Lev Aslanovich Tarasov, (Russian: Лев Асланович Тарасов, Lev Aslanovich Tarasov) in Moscow to parents of mixed heritage, including Armenian, Russian, German and Georgian. According to his autobiography he states that his surname is Armenian (Torossian), while his maternal grandmother was German and his maternal grandfather was of mixed Georgian and Armenian descent. His family fled Russia after the outbreak of the revolution. After a long exodus taking them to the Caucasus on to Crimea and later by sea to Istanbul and then Venice, the family finally settled in Paris in 1920, where young Troyat was schooled and later earned a law degree. The stirring and tragic events of this flight across half of Europe are vividly recounted by Troyat in Tant que la terre durera. His first marriage produced a son before ending in divorce. He later married the love of his life, a widow with a young daughter whom he raised as his own.
Troyat received his first literary award, Le prix du roman populaire, at the age of twenty-four, and by twenty-seven, he was awarded the Prix Goncourt. He published more than 100 books, novels and biographies, among them those of Anton Chekhov, Catherine the Great, Rasputin, Fyodor Dostoyevsky, Ivan the Terrible and Leo Tolstoy. Troyat's best-known work is La neige en deuil, which was adapted as an English-language film in 1956 under the title The Mountain.
Troyat was elected as a member of the Académie française in 1959. At the time of his death, he was the longest-serving member.