Gary was born Roman Kacew (Yiddish: קצב, Russian: Рома́н Ка́цев) in Vilnius, Lithuania (at that time in the Russian Empire). In his books and interviews, he presented many different versions of his parents' origins, ancestry, occupation and his own childhood. His mother, Mina Owczyńska (1879—?), was a Russian actress from Švenčionys and his father was a businessman Arieh-Leib Kacew (1883—1942) from Trakai, also a Lithuanian Jew. Arieh Leib abandoned the family in 1925 and remarried. Gary later claimed that his actual father was the celebrated actor and film star Ivan Mosjoukine, with whom his actress mother had worked and to whom he bore a striking resemblance. Mosjoukine appears in his memoir Promise at Dawn. When Gary was fourteen, he and his mother moved to Nice, France. Converted to Catholicism by his mother, Gary studied law, first in Aix-en-Provence and then in Paris. He learned to pilot an aircraft in the French Air Force in Salon-de-Provence and in Avord Air Base, near Bourges.
Following the Nazi occupation of France in World War II, he fled to England and under Charles de Gaulle served with the Free French Forces in Europe and North Africa. As a bombardier-observer in the Groupe de bombardement Lorraine (No. 342 Squadron RAF), he took part in over 25 successful sorties, logging over 65 hours of air time. During this time, he changed his name to Romain Gary. He was decorated for his bravery in the war, receiving many medals and honours, including Compagnon de la Libération and commander of the Légion d'honneur. In 1945 he published his first novel, Education européenne. Immediately following his service in the war, he worked in the French diplomatic service in Bulgaria and Switzerland. In 1952 he became the secretary of the French Delegation to the United Nations. In 1956, he became Consul General in Los Angeles and became acquainted with Hollywood.
Gary became one of France's most popular and prolific writers, authoring more than thirty novels, essays and memoirs, some of which he wrote under a pseudonym.
He is the only person to win the Prix Goncourt twice. This prize for French language literature is awarded only once to an author. Gary, who had already received the prize in 1956 for Les racines du ciel, published La vie devant soi under the pseudonym Émile Ajar in 1975. The Académie Goncourt awarded the prize to the author of that book without knowing his identity. Gary's cousin's son Paul Pavlowitch posed as the author for a time. Gary later revealed the truth in his posthumous book Vie et mort d'Émile Ajar. Gary also published as Shatan Bogat, Rene Deville and Fosco Sinibaldi, as well as his birth name Roman Kacew.
In addition to his success as a novelist, he wrote the screenplay for the motion picture The Longest Day and co-wrote and directed the film Kill! (1971), which starred his wife at the time, Jean Seberg. In 1979, he was a member of the jury at the 29th Berlin International Film Festival.
Gary's first wife was the British writer, journalist, and Vogue editor Lesley Blanch, author of The Wilder Shores of Love. They married in 1944 and divorced in 1961. From 1962 to 1970, Gary was married to American actress Jean Seberg, with whom he had a son, Alexandre Diego Gary. According to Diego Gary, he was a distant presence as a father: "Even when he was around, my father wasn't there. Obsessed with his work, he used to greet me, but he was elsewhere."
After learning that Jean Seberg had an affair with Clint Eastwood, Gary challenged him to a duel, but Eastwood declined.
Gary died of a self-inflicted gunshot wound on 2 December 1980 in Paris. He left a note which said that his death had no relation to Seberg's suicide the previous year. He also stated in his note that he was Émile Ajar.
Gary was cremated in Père Lachaise Cemetery and his ashes were scattered in the Mediterranean Sea near Roquebrune-Cap-Martin.Les oiseaux vont mourir au Pérou (Birds in Peru) (1968) starring Jean Seberg
Kill! Kill! Kill! Kill! (1971) also starring Jean Seberg
The Roots of Heaven (1958)
The Longest Day (1962)