Seán Lester (28 September 1888 – 13 June 1959) was an Irish diplomat who was the last secretary-general of the League of Nations from 31 August 1940 to 18 April 1946.
The family moved to Belfast when he was young and he attended Methodist College Belfast in the city; after leaving school, he changed his name from John to the Irish ‘Seán’.
As a young man, he joined the Irish Republican Brotherhood (IRB). Lester often represented the Irish Free State at Council meetings and stood in for the Irish Minister for External Affairs. He became increasingly involved in the work of the League, particularly in its attempts to bring a resolution to two wars in South America. His work brought him to the attention of the League Secretariat and began his transformation from national to international civil servant.
When Peru and Colombia had a dispute over a town in the headwaters of the Amazon, Lester presided over the committee that found an equitable solution; he also presided over the less-successful committee when Bolivia and Paraguay went to war over the Gran Chaco.
In August 2010, a room in the Gdańsk City Hall, the building that had been Lester's headquarters during his stay, was renamed by Mayor Paweł Adamowicz as the Seán Lester Room.
League of Nations
Lester returned to Geneva in 1937 to become Deputy Secretary General of the League of Nations. In 1940, he became Secretary General of the body
His granddaughter Susan Denham was Chief Justice of Ireland for the Supreme Court of Ireland from 2011 to 2017.
In 2013, the Ulster History Circle secured a plaque for his childhood home in Belfast.