Alexander Kerensky was born in Simbirsk (now Ulyanovsk) on the Volga River into the family of a secondary school principal. Fyodor Kerensky, whose father was a teacher. His mother, Nadezhda Adler, was the daughter of a nobleman, Alexander Adler, head of the Topographical Bureau of the Kazan Military District. Her mother, Nadezhda Kalmykova, was the daughter of a former serf who had bought his freedom before serfdom was abolished in the 19th century, allowing him to become a wealthy Moscow merchant. Kerensky's father was the headmaster of Vladimir Ulyanov (Lenin) at a secondary school for boys in Simbirsk, and members of the Kerensky and Ulyanov families were friends. In 1889, when Kerensky was eight, his family moved to Tashkent, where his father had been appointed the main inspector of public schools (superintendent). Kerensky graduated with honors from a Tashkent secondary school in 1899.

The same year he entered St. Petersburg University, where he studied history and philology in his first year. The next year he switched to the Law Department and received a law degree in 1904, getting married in the same year to the daughter of a Russian general. He worked as a legal counsel to victims of government violence in early December 1905. At the end of the month he was jailed on suspicion of belonging to a militant group. Afterwards he gained a reputation for his work as a defense lawyer in a number of political trials of revolutionaries.

He was elected to the Fourth Duma in 1912 as a member of the Trudoviks, a moderate labour party who were associated with the Socialist Revolutionary Party. He was a brilliant orator and skilled parliamentary leader as a Socialist Revolutionary and a leader of the socialist opposition to the regime of the ruling Tsar, Nicholas II. When the February Revolution broke out in 1917, Kerensky was one of its most prominent leaders: he was member of the Provisional Committee of the State Duma and was elected vice-chairman of the Petrograd Soviet. He simultaneously became the first Minister of Justice in the newly formed Provisional Government. When the Soviet passed a resolution prohibiting its leaders from joining the government, Kerensky delivered a stirring speech at a Soviet meeting. Although the decision was never formalized, he was granted a de facto exemption and continued acting in both capacities.

After the first government crisis over Pavel Milyukov's secret note re-committing Russia to its original war aims on May 2–4, Kerensky became the Minister of War and the dominant figure in the newly formed socialist-liberal coalition government. On 10 May (Old Style), Kerensky started for the front, and visited one division after another, urging the men to do their duty. His speeches were impressive and convincing for the moment, but had little lasting effect. Under Allied pressure to continue the war, he launched what became known as the Kerensky Offensive against the Austro-Hungarian/German South Army on 17 June Old Style. At first successful, the offensive was soon stopped and then thrown back by a strong counter-attack. The Russian Army suffered heavy losses and it was clear – from many incidents of desertion, sabotage, and mutiny – that the Russian Army was no longer willing to attack. Kerensky was heavily criticised by the military for his liberal policies, which included stripping officers of their mandate (handing overriding control to revolutionary inclined "soldier committees" instead), the abolition of the death penalty, and the presence of various revolutionary agitators at the front. Many officers jokingly referred to commander in chief Kerensky as "persuader in chief".

On 2 July 1917, the first coalition collapsed over the question of Ukraine's autonomy. Following July Days unrest in Petrograd and suppression of the Bolsheviks, Kerensky succeeded Prince Lvov as Russia's Prime Minister. Following the Kornilov Affair at the end of August and the resignation of the other ministers, he appointed himself Supreme Commander-in-Chief as well. Kerensky's next move, on 15 September was to proclaim Russia a republic, which was quite contrary to the understanding that the Provisional Government should only hold power until the Constituent Assembly should meet to decide Russia's form of rule. He formed a five-member Directory, which consisted of Kerensky himself, minister of foreign affairs Mikhail Tereshchenko, minister of war general Verkhovsky, minister of navy admiral Dmitry Verderevsky and minister of post and telegraph Nikitin. He retained his post in the final coalition government in October 1917 until it was overthrown by the Bolsheviks.

Kerensky's major challenge was that Russia was exhausted after three years of war, while the provisional government did not offer much motivation for a victory outside of continuing Russia's obligations towards its allies. Furthermore, Lenin and his Bolshevik party were promising "peace, land, and bread" under a communist system. The army was disintegrating due to a lack of discipline, which fostered desertion in large numbers. Kerensky and the other political leaders continued their obligation to Russia's allies by continuing involvement in World War I – fearing that the economy, already under huge stress from the war effort, might become increasingly unstable if vital supplies from France and the United Kingdom were to be cut off. Some also feared that Germany would demand enormous territorial concessions as the price for peace (which indeed happened in the Treaty of Brest-Litovsk). The dilemma of whether to withdraw was a great one, and Kerensky's inconsistent and impractical policies further destabilized the army and the country at large. Furthermore, Kerensky adopted a policy that isolated the right-wing conservatives, both democratic and monarchist-oriented. His philosophy of "no enemies to the left" greatly empowered the Bolsheviks and gave them a free hand, allowing them to take over the military arm or "voyenka" of the Petrograd and Moscow Soviets. His arrest of Kornilov and other officers left him without strong allies against the Bolsheviks, who ended up being Kerensky's strongest and most determined adversaries, as opposed to the right wing, which evolved into the White movement.

During the Kornilov Affair, Kerensky had distributed arms to the Petrograd workers, and by October most of these armed workers had gone over to the Bolsheviks. On 25–27 October (Old Style) 1917 the Bolsheviks launched the second Russian revolution of the year. Kerensky's government in Petrograd had almost no support in the city. Only one small force, the First Petrograd Women's Battalion, was willing to fight for the government against the Bolsheviks, but this force too crossed over to the revolution without firing a single shot. It took less than 20 hours before the Bolsheviks had taken over the government. Kerensky escaped the Bolsheviks and went to Pskov, where he rallied some loyal troops for an attempt to retake the capital. His troops managed to capture Tsarskoe Selo, but were beaten the next day at Pulkovo. Kerensky narrowly escaped, and spent the next few weeks in hiding before fleeing the country, eventually arriving in France. During the Russian Civil War he supported neither side, as he opposed both the Bolshevik regime and the White Movement.

Kerensky lived in Paris until 1940, engaged in the endless splits and quarrels of the exiled Russian democratic leaders. In 1939, Kerensky married the former Australian journalist Lydia ‘Nell' Tritton. When the Germans overran France at the start of World War II, they escaped to the United States. Tritton and Kerensky married at Martins Creek, Pennsylvania. In 1945, his wife became terminally ill. He traveled with her to Brisbane, Australia, and lived there with her family; she suffered a stroke in February, and they remained there until her death on 10 April 1946. Thereafter Kerensky returned to the United States, where he spent the rest of his life. When Adolf Hitler's forces invaded the Soviet Union in 1941, Kerensky offered his support to Stalin, but received no reply. Instead, he made broadcasts in Russian in support of the war effort. Kerensky eventually settled in New York City, but spent much of his time at the Hoover Institution at Stanford University in California, where he both used and contributed to the Institution's huge archive on Russian history, and where he taught graduate courses. He wrote and broadcast extensively on Russian politics and history. His last public speech was delivered at Kalamazoo College, in Kalamazoo, Michigan.

Kerensky died at his home in New York City in 1970, one of the last surviving major participants in the turbulent events of 1917. The local Russian Orthodox Churches in New York refused to grant Kerensky burial, seeing him as being a freemason and being largely responsible for Russia falling to the Bolsheviks. A Serbian Orthodox Church also refused. Kerensky's body was then flown to London where he was buried at Putney Vale's non-denominational cemetery.