Seán Lemass had been Éamon de Valera's "heir-apparent" since his appointment as Tánaiste in 1945. It was widely assumed amongst the general public, and was an accepted fact within the Fianna Fáil party that Lemass would succeed de Valera whenever "the Chief" decided to retire. In 1959 that opportunity arose when de Valera was elected President of Ireland.
There were several other contenders for the post of party leader. In the 1930s and 1940s Seán MacEntee was considered Lemass's closest rival for the top job. However, his poor performance as Minister for Finance in the 1950s discredited his reputation. Frank Aiken was also considered a very able Foreign Minister and a potential candidate. The British embassy in Dublin kept London informed of the changes. They speculated that Aiken and Lemass would be the two main contenders, however, James Ryan would be elected as a compromise candidate. However, the divisions that they believed existed between Lemass and Aiken were not true.
When the Fianna Fáil parliamentary party met on 22 June Seán MacEntee proposed Lemass as leader, with Frank Aiken seconding the motion. Seán Lemass was thus elected the second leader of Fianna Fáil.