Alan de Lastic was born in Maymyo, Burma on 24 September 1929. He was of mixed Burmese, Irish and French ancestry, with his grandparents on his father's side coming from Bourg-Lastic in France, but he always considered himself wholly Indian. In 1942 his family escaped from Rangoon when the Japanese army entered Burma during the World War II.de Lastic completed his secondary education in Patna, then moved to Calcutta where he spent five years studying marine engineering. He worked in the Calcutta shipyards before being called to the priesthood. de Lastic began his ecclesiastical studies in 1951. He was ordained on 21 December 1958 as a priest in Calcutta. He went to Rome, where he completed his doctorate in dogmatic theology, and then spent a year at University College Dublin in Ireland, returning to India in the early 1960s.

de Lastic rose quickly in the hierarchy of the Catholic Church of India. On 9 April 1979 he was appointed Auxiliary Bishop of Calcutta, and on 9 April 1979 was appointed Titular Bishop of Cissa. Mother Teresa was present at the ceremony in the Vatican when Pope John Paul II consecrated Alan as a Bishop on 27 May 1979.On 2 July 1984 he was appointed Bishop of Lucknow, and on 19 November 1990 he was appointed Archbishop of Delhi. He assumed office as archbishop on 27 January 1991.In 1998 he was appointed President of the Catholic Bishops' Conference of India. Alan de Lastic died on 20 June 2000 in a car crash in Poland. His funeral was held on 27 June 2000 in Delhi and was attended by about 15,000 people, far more than anticipated. In addition to over 70 bishops, 400 priests and hundreds of nuns the funeral was attended by representatives of Bahais, Buddhists, Hindus, Jains, Jews, Muslims, Sikhs and Zoroastrians. President of India K. R. Narayanan, Congress Party leader Sonia Gandhi and several federal ministers paid their respects.