Tolstoy was born in Yasnaya Polyana, the family estate in the Tula region of Russia. The Tolstoys were a well-known family of old Russian nobility. He was the fourth of five children of Count Nikolai Ilyich Tolstoy, a veteran of the Patriotic War of 1812, and Countess Mariya Tolstaya (Volkonskaya). Tolstoy's parents died when he was young, so he and his siblings were brought up by relatives. In 1844, he began studying law and oriental languages at Kazan University. His teachers described him as "both unable and unwilling to learn." Tolstoy left university in the middle of his studies, returned to Yasnaya Polyana and then spent much of his time in Moscow and Saint Petersburg. In 1851, after running up heavy gambling debts, he went with his older brother to the Caucasus and joined the army. It was about this time that he started writing.

His conversion from a dissolute and privileged society author to the non-violent and spiritual anarchist of his latter days was brought about by his experience in the army as well as two trips around Europe in 1857 and 1860–61. Others who followed the same path were Alexander Herzen, Mikhail Bakunin, and Peter Kropotkin. During his 1857 visit, Tolstoy witnessed a public execution in Paris, a traumatic experience that would mark the rest of his life. Writing in a letter to his friend Vasily Botkin: "The truth is that the State is a conspiracy designed not only to exploit, but above all to corrupt its citizens ... Henceforth, I shall never serve any government anywhere."

His European trip in 1860–61 shaped both his political and literary transformation when he met Victor Hugo, whose literary talents Tolstoy praised after reading Hugo's newly finished Les Miserables. A comparison of Hugo's novel and Tolstoy's War and Peace shows the influence of the evocation of its battle scenes. Tolstoy's political philosophy was also influenced by a March 1861 visit to French anarchist Pierre-Joseph Proudhon, then living in exile under an assumed name in Brussels. Apart from reviewing Proudhon's forthcoming publication, La Guerre et la Paix (War and Peace in French), whose title Tolstoy would borrow for his masterpiece, the two men discussed education, as Tolstoy wrote in his educational notebooks: "If I recount this conversation with Proudhon, it is to show that, in my personal experience, he was the only man who understood the significance of education and of the printing press in our time."

Fired by enthusiasm, Tolstoy returned to Yasnaya Polyana and founded thirteen schools for his serfs' children, based on the principles Tolstoy described in his 1862 essay "The School at Yasnaya Polyana". Tolstoy's educational experiments were short-lived, partly due to harassment by the Tsarist secret police. However, as a direct forerunner to A. S. Neill's Summerhill School, the school at Yasnaya Polyana can justifiably be claimed to be the first example of a coherent theory of democratic education.

On 23 September 1862, Tolstoy married Sophia Andreevna Behrs, who was 16 years his junior and the daughter of a court physician. She was called Sonya, the Russian diminutive of Sofya, by her family and friends. They had thirteen children.

The marriage was marked from the outset by sexual passion and emotional insensitivity when Tolstoy, on the eve of their marriage, gave her his diaries detailing his extensive sexual past and the fact that one of the serfs on his estate had borne him a son.Even so, their early married life was ostensibly happy and allowed Tolstoy much freedom to compose War and Peace and Anna Karenina with Sonya acting as his secretary, proof-reader and financial manager. However, their latter life together has been described by A. N. Wilson as one of the unhappiest in literary history. Tolstoy's relationship with his wife deteriorated as his beliefs became increasingly radical. This saw him seeking to reject his inherited and earned wealth, including the renunciation of the copyrights on his earlier works.

Tolstoy died in 1910, at the age of 82. He died of pneumonia at Astapovo train station, after falling ill when he left home in the middle of winter. His death came only days after gathering the nerve to abandon his family and wealth and take up the path of a wandering ascetic,[citation needed] a path that he had agonized over pursuing for decades. He had not been at the peak of health before leaving home; his wife and daughters were all actively engaged in caring for him daily. He had been speaking and writing of his own death in the days preceding his departure from home, but fell ill at the station not far from home. The station master took Tolstoy to his apartment, where his personal doctors were called to the scene. He was given injections of morphine and camphor.

The police tried to limit access to his funeral procession, but thousands of peasants lined the streets at his funeral. Still, some peasants were heard to say that, other than knowing that "some nobleman had died," they knew little else about Tolstoy.