He was born in Beirut, the son of Pierre Gemayel, founder of the Lebanese Kataeb party, or Phalangist Party, a right-wing organization that, although officially secular, was supported almost entirely by Maronite Christians. Bashir was educated at the Lebanese Modern Institute. In 1962, he joined the Kataeb party. He completed his formal education at St. Joseph University in Beirut after teaching for three years at the Lebanese Modern Institute, graduating in 1971 with a degree in Law and another in Political Science in 1973. A year prior to that, in 1970, he had been briefly kidnapped by Palestinian militants, in an incident that may have influenced his later hostility to the Palestinian cause.
In 1971, he was appointed inspector in the para-military branch of the Kataeb party, the Kataeb Regular Forces. In 1971 he also took another law qualification from the American and International Law Academy in Dallas, Texas. Qualifying in 1972 he joined the bar association and opened an office in West Beirut. However, outside of his legal work in 1974, he founded the "BG squad", a Lebanese militia, to face the PLO. In 1976, he became president of the Kataeb Military Council and formed the Unified Lebanese Forces to combat Syrian advances. In 1978 he led the "Hundred Days War" against Syrian forces. Gemayel became a member of the Lebanese Front in 1980 and in 1981 he led the unified Christian Lebanese militias in the Battle of Zahleh. In his military campaigns, Gemayel secretly accepted military supplies from Israel, and is widely believed, despite public denials, to have accepted Israeli training for his troops.
Israeli forces invaded Lebanon in 1982. Although Gemayel did not cooperate with the Israelis publicly, his long history of tactical collaboration with Israel, whether real or suspected, counted against him in the eyes of many Lebanese Moslems. Although the only announced candidate for the presidency of the republic, the National Assembly elected him by the second narrowest margin in Lebanese history (57 votes out of 92) on August 23, 1982; most Moslem members of the Assembly boycotted the vote. Nine days before he was due to take office, Gemayel was killed along with twenty-five others in an explosion at the Kataeb headquarters in Achrafieh on September 14, 1982. He was succeeded as president by his older brother Amine Gemayel, who served from 1982 to 1988. Rather different in temperament, Amine Gemayel was widely regarded as lacking the charisma and decisiveness of his brother, and many of the latter's followers were dissatisfied.
More than 21 years after his assassination, Bachir Gemayel remains a divisive figure in Lebanese politics. Many right-wing Christians remember him nostalgically as a hero, seeing him as the embodiment of what Lebanon could and should have been. Others disagree, pointing out that his cause was ultimately on the losing side of the Lebanese Civil War of 1975-1990. His widow, Solange Gemayel works to keep his legacy alive through the Bachir Gemayel Foundation, a political and informational organization. His first daughter, Maya was killed by a car bomb intended for Gemayel himself in 1979, when Maya was eighteen months old. He has two surviving children: a daughter, Youmna, who is now a political science student in Paris, and a son, Nadim, a law student and political activist. Nadim recently attracted controversy when he went against virtually the entire political establishment by endorsing an antigovernment candidate in an important byelection in Baabda-Aley.