The Tánaiste (/ˈtɔːnɪʃtə/ TAW-nish-tə,^[3] Irish: [ˈt̪ˠaːn̪ˠəʃtʲə] ^ⓘ) is the second-ranking member of the government of Ireland and the holder of its second-most senior office.^[4][5] They are the equivalent of a deputy prime minister in other parliamentary systems.

The Tánaiste is appointed by the President of Ireland on the advice of the Taoiseach. The current office holder is former Taoiseach Micheál Martin, TD, who was appointed on 17 December 2022.^[6]

Under the Gaelic system of tanistry, the word tánaiste (plural tánaistí, pronounced [ˈt̪ˠaːn̪ˠəʃtʲiː], approximately /ˈtɔːnɪʃtiː/) had been used for the heir of the chief (taoiseach) or king (rí).^{[citation needed]} The word was adopted in the 1937 Constitution of Ireland as the title for a member of the government nominated by the Taoiseach to act in their place as needed during periods of the Taoiseach's temporary absence. Tánaiste is the official title of the deputy head of government in both English and Irish, and is not used for other countries' deputy prime ministers, who are referred to in Irish by the generic term leas-phríomh-aire, pronounced [ˈl̠ʲasˠ ˌfʲɾʲiːw ˈaɾʲə], approximately /ˌlæsfriːˈvɛərə/ LASS-free-VAIR-ə. The longer Irish form, an Tánaiste, is sometimes used in English instead of "the Tánaiste".

The office was created in 1937 under the new Constitution of Ireland and replaced the previous office of Vice-President of the Executive Council, which had existed under the Constitution of the Irish Free State, and which was first held by Kevin O'Higgins of Cumann na nGaedheal from 1922 to 1927.

The Taoiseach nominates one member of the Government to the office who is required to be a member of Dáil Éireann.^[7] The nominee then receives their seal of office from the President of Ireland in recognition of the appointment. The Tánaiste acts in the place of the Taoiseach during a temporary absence. In the event of the Taoiseach's death or permanent incapacitation, the Tánaiste acts as Taoiseach until another is appointed.^[8] The Tánaiste is, ex officio, a member of the Council of State. The Tánaiste chairs meetings of the government in the absence of the Taoiseach and may take questions on their behalf in the Dáil or Seanad.

Aside from those duties, the title is largely honorific as the Constitution does not confer any additional powers on the office holder over and above the other members of the Government. In theory, the Tánaiste could be a minister without portfolio, but every Tánaiste has in parallel held a ministerial portfolio as head of a Department of State. The Department of the Taoiseach is a Department of State, but there is no equivalent for the Tánaiste. Dick Spring in the Rainbow Coalition (1994–1997) had an official "Office of the Tánaiste", but other parties have not used that nomenclature.Connolly, Eileen (2005). "The government and the governmental system". In Coakley, John; Gallagher, Michael (eds.). Politics in the Republic of Ireland. Psychology Press. pp. 339–340. ISBN 9780415280662. Retrieved 20 April 2016. Under Spring, Eithne Fitzgerald was "Minister of State at the Office of the Tánaiste", with responsibility for co-ordinating Labour policy in the coalition.^[9][10]

Under a coalition government, the Tánaiste is typically the leader of the second-largest coalition partner, just as the Taoiseach is usually leader of the coalition's senior partner. However, during the coalition governments in 1989–1992 and 2007–2011, the position was held by Fianna Fáil's deputy leader, rather than the leader of a junior partner. As part of a rotating Taoiseach agreement since 2020, the role of Tánaiste gained increased prominence and responsibility in coordinating and Government policy as it was held by Leo Varadkar for the first half of the Government's term in office prior to his appointment as Taoiseach and Micheál Martin in the second half.^[11]

The office of Tánaiste is as yet the highest government rank attained by a woman Minister.^[12]

Four Tánaistí later held the office of Taoiseach: Seán Lemass, Bertie Ahern, Brian Cowen, and Leo Varadkar (his second term as Taoiseach). Varadkar is also one of two Tánaistí, with Micheál Martin, to have previously held the office of Taoiseach before becoming Tánaiste. Two Tánaistí were later elected as President of Ireland: Seán T. O'Kelly and Erskine H. Childers.