The 21st Dáil met at Leinster House on 5 July to nominate the Taoiseach for appointment by the president and to approve the appointment of a new government of Ireland. Jack Lynch was appointed Taoiseach, forming the 15th government of Ireland, a single-party majority Fianna Fáil government. It was the last election to result in a single-party majority government.
Although it had faced some controversial issues during its term of office, the ruling Fine Gael–Labour Party coalition had hoped to defy political history by winning an unprecedented second term. This belief was further augmented following the so-called "Tullymander" of parliamentary constituencies, referring to a scheme drawn up by James Tully, the Minister for Local Government, redrawing constituencies across the country to maximise the vote for the coalition partners. For example, in Dublin there were thirteen three-seat constituencies. It was hoped that the coalition partners would win two of the seats, leaving Fianna Fáil with only one seat. A similar tactic was used in rural areas where the party was at its strongest.
The government parties of Fine Gael and the Labour Party fought the general election on their record in government. The redrawing of the constituency boundaries gave them hope for success.
Fianna Fáil and its leader Jack Lynch believed that they were not likely to win the general election. The party drew up a manifesto which offered the electorate a string of financial and economic "sweeteners", encouraging them to vote for Fianna Fáil. Some of the promises that were offered included abolition of rates on houses, abolition of car tax and a promise to reduce unemployment to under 100,000. Lynch agreed to the manifesto because he believed that the party needed something dramatic if it were to win the election.
The Fianna Fáil campaign was based on the American model. Inspired by director of elections Séamus Brennan, Lynch travelled the length and breadth of the country, music blaring, accompanied by his followers. His popularity was at its highest; Lynch's popularity was a big electoral asset. The party slogan "Bring Back Jack" even played on Lynch's huge appeal. But the monetary sweeteners were Fianna Fáil's biggest asset. And it soon became clear the party might win the election.
While towards the end of the campaign Fianna Fáil were expected to win the general election, nobody predicted the scale of that victory. An unprecedented nine-seat majority in Dáil Éireann for Fianna Fáil saw the National Coalition swept from power in what was at the time the biggest political hurricane in Irish history. Only Éamon de Valera had ever done better, but only once out of 13 elections. Following the election, the leaders of Fine Gael and the Labour Party, Liam Cosgrave and Brendan Corish resigned as leaders of their respective parties, the first occasion in which a defeated Taoiseach or Tánaiste had done so.
The increased popularity of FF produced by its leader's popularity and by the unprecedented sweeteners, were the cause for the scale of the coalition's defeat. Unhappy with the "Tullymander", the new government established an independent commission to revise constituency boundaries, adding members overall and replacing many 3-seat districts with 4- or 5-seat districts.