Colin Eglin was born on 14 April 1925 in Sea Point, Cape Town. His father died when he was nine years old and he had to move to live with his aunt in the Eastern Free State of South Africa, where he attended school; he was the only English-speaking student.

In the mid-1930s, the political tensions between the two leaders of the South African United National Party spilled over into the very life of his aunt's family, such that Colin, disagreeing with her ideas, moved to the college in Villiersdorp, where he graduated in 1939. The following year he enrolled at the University of Cape Town, taking a course in Quantity Surveying. In 1943, at the age of 18, he interrupted his studies to join the army as a volunteer. He first became an instructor in the Cape Town anti-aircraft unit, then was transferred to Egypt where he joined the 6th South African Armoured Division, where he served in the First City/Cape Town Highlanders regiment until the end of the war.

In 1946, he returned to South Africa, where he completed his studies and graduated with a degree in Quantity Surveying. In 1949, he married Joyce Mabel, and together they had three daughters. In 1951, he became president of the Pinelands Civic Association and was elected to the town's municipal council. In 1954, he became a provincial councillor for the United Party and remained so until 1958. Later, in 1959, he became one of the founders of the new Progressive Party (PP). In 1971 he became president of the National Executive Branch of the PP. From 1971 to 1994 Eglin led the Democratic Alliance, a multi-racial party that achieved small but significant victories, such as being allowed to visit Steve Biko in prison before the activist was killed by police beatings in 1977. Eglin's party was the first to send a delegation of whites to the so-called 'Southern Homelands', where blacks were relegated, to begin a dialogue on the future of South Africa. The Progressive Reform Party he led became an authoritative mediator between the 10 million whites, the 37 million blacks and their respective political representatives.

Colin Eglin died on 29 November 2013. Nelson Mandela described him as one of the architects of democracy in South Africa.