[9] In 1961, his parents moved to Ghana in West Africa, where he had his primary education at Christ the King International School.

[12] Alagiah returned to his grandfather's original home in Sri Lanka in the aftermath of the 2004 Indian Ocean earthquake and tsunami to survey the damage.

[10] As one of the BBC's leading foreign correspondents, he reported on events ranging from the genocide in Rwanda to the plight of the Marsh Arabs in southern Iraq, as well as the civil wars in Afghanistan, Liberia, Sierra Leone, Kosovo, and Somalia.

[15] In October 2011, Alagiah presented Mixed Britannia, a three-part documentary series on the history of interracial marriage in the United Kingdom.

[16] A specialist on Africa and the developing world, Alagiah interviewed, among others, Nelson Mandela, Archbishop Desmond Tutu, former Secretary-General of the United Nations Kofi Annan and President Robert Mugabe of Zimbabwe.

[13] In 2000, Alagiah was part of the BBC team which collected a BAFTA award for its coverage of the Kosovo conflict.

[20] From 2002 to 2009, Alagiah was a patron of The Fairtrade Foundation,[21] but in July 2009 he was obliged to resign by BBC Management, who claimed professional conflict of interest.

The BBC responded that in keeping with its principles of impartiality, it would be inappropriate for one of its leading journalists to be seen supporting a movement that clearly represents a controversial view of global trade.

[30][38] In June 2020, Alagiah said that the cancer had spread to his lungs, liver and lymph nodes, but was not at a "chronic" or "terminal" stage.

[40] In October 2022, Alagiah announced that his cancer had spread further; he subsequently took a break from television to undergo a new course of treatment.