Martin George Southcote Mansergh (born 31 December 1946) is an Irish former Fianna Fáil politician who served as a Minister of State from 2008 to 2011.

Later recruited by Taoiseach Charles Haughey, he worked for the Fianna Fáil party thereafter, serving under three Fianna Fáil leaders as Director of Research, Policy and Special Advisor on Northern Ireland where he was involved in discussions between the nationalist parties and the Irish Government and met regularly with intermediary Father Alec Reid.

[6] As a senior adviser[6] to successive Taoisigh, Mansergh has played a key role in the Northern Ireland peace process over the last twenty years.

[9][10][11] In January 2009, he offered to quit his junior ministry post to save money and called on people to retain their Celtic Tiger style optimism and self-respect.

[18] In February 2008, on the RTÉ Radio 1 show Morning Ireland, Mansergh insisted that Ahern's difficulties were no more than a spot of "inflight turbulence," with a safe landing in sight.

"[19] Mansergh is mentioned by name in the TV series, Charlie, where Taoiseach, Charles Haughey, in a conversation with Fr Alec Reid, places him in charge of drawing up a roadmap to peace in Northern Ireland.

[22] Carlow College awarded its inaugural St. Columbanus Medal in November 2018, to Mansergh, in recognition of his contribution to the peace process in Ireland.