De Valera's advancing age and identity with the last three decades of the state's history was increasingly becoming a hinderance to Fianna Fáil, which wished to contest the upcoming general election with a new face in charge. As well as this, questions were arising over de Valera's involvement with the Irish Press newspaper, which he founded and directed up to this point - simultaneous with his service as Taoiseach. In the face of this controversy and the reality of his age, de Valera reluctantly agreed to step down as Taoiseach and become the Fianna Fáil nominee for President.
De Valera's vote shares

De Valera won a majority of the vote in every constituency bar the northern Dublin city constituencies, Longford-Westmeath, which Mac Eoin had represented for over ten years, and Cork West, a strong Fine Gael area. As in the previous election, Mac Eoin's best results were in the Longford and surrounding areas, with strong results also where de Valera didn't win majorities in Dublin. De Valera's vote was strongest in Clare, Galway and Donegal - his share reaching 69% in parts of the latter two counties.
De Valera was accordingly elected the third President of Ireland. He had moved from the frontlines of Irish politics to what was quitely being called the "retirement home". This was not the end of his life in the political scene however, as the next decade would see him step to the forefront yet again, this time as a representative rather than a leader.
Full results:
Éamon de Valera (Fianna Fáil) - 538,003 (56.3%)
Seán Mac Eoin (Fine Gael) - 417,536 (43.7%)