Born as Isaac Blank in Germiston, South Africa, he was introduced to Trotskyism by a lodger at his parent's house, and by the Militant publication of the Communist League of America. In 1934, he helped found a small Trotskyist group, but later in the year, decided to move to London where he believed there were better prospects for the movement.
On the journey, Isaac changed his name to Ted Grant, and stopped over in France to meet Trotsky's son, Leon Sedov. Once in Britain, he joined the Marxist Group, which at the time was working in the Independent Labour Party and took part in the Battle of Cable Street against fascists. But when Trotsky suggested the group should turn to working in the Labour Party, and their leadership disagreed, Grant was one of a small group who split to form the Bolshevik-Leninist Group, which soon became known as the Militant Group. The group grew, but in 1937, a dispute about the leadership's treatment of some new comrades led to the expulsion of several members, including Grant.
The expelled members formed the Workers International League, and Grant became its increasingly important theoretician. The group grew, and in 1941, he became editor of its paper. He continued his role in the fused Revolutionary Communist Party. Upon its beak-up, Grant reluctantly joined Gerry Healy's faction, but was soon expelled. He formed a new, small tendency in the Labour Party, which in 1953 was recognised at the official British section of the Fourth International. The group at first grew only very slowly, but by 1983, when it was known as the Militant Tendency, it was a significant force in British politics, and Grant was expelled from the Labour Party. After turmoil in the group, Grant left in 1992 to form Socialist Appeal, and has devoted much of his time to writing.