Mansergh entered the
Department of Foreign Affairs, being appointed a Third secretary in 1974 and became a First Secretary in 1977. 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. He was a key member of the team which formed the
Fianna Fáil–
Labour Party coalition in 1992 and was also involved in the formation of the Fianna Fáil–
Progressive Democrats coalition in 1997. As a senior adviser to successive
Taoisigh, Mansergh played a key role in the
Northern Ireland peace process for over twenty years. He ran for Fianna Fáil as a Dáil candidate in the Tipperary South constituency at the
2002 general election but failed to be elected with 14.2% of the poll. However, Mansergh was elected to the
22nd Seanad by the
Agricultural Panel in July of that year. At the
2007 general election he again ran for Fianna Fáil as a
Dáil candidate in the Tipperary South constituency, this time being elected with 15.7% of the poll. He was
appointed to the
Council of State by President
Mary McAleese and served from 2004 to 2011. Until 2006 he wrote a weekly column for
The Irish Times, but resigned because of the upcoming general election. In May 2008, he was appointed by
the government of
Brian Cowen as
Minister of State at the Department of Finance with special responsibility for the
Office of Public Works and
Minister of State at the Department of Arts, Sport and Tourism with special responsibility for the Arts. 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. He said: "We're not going to get anywhere by completely throwing overboard our self respect. We have achieved a tremendous amount in the past 20 years – they were the best 20 years in our history. There will be cycles – we rose very high and we are where we are now. We have to work our way out of this intelligently". However, he was re-appointed to his positions when Cowen reduced the number of junior ministers from 20 to 15. Mansergh lost his seat at the
2011 general election. He had been a frequent contributor to
The Irish Catholic. ==Media image==