- 1899 – Born in Dublin on 15 July
- 1916 - Takes part in the Easter Rising
- 1920 – Interned at Ballykinlar, Co Down as the War of Independence ensued
- 1924 – First elected to Dáil Éireann
- 1926 - Member of the organising committee and a founder member of Fianna Fáil
- 1932 – At the age of thirty-two Lemass becomes the youngest cabinet minister in Europe, becoming Minister for Industry and Commerce.

- 1945 –Becomes Tánaiste
- 1958 –Introduces the first Programme for Economic Expansion which lifts the Irish economy
- 1965 – Lemass meets Northern Premier Captain Terence O’Neill at Stormont in an attempt to improve relations between North and South
- 1965 – Fianna Fáil remain in government following a successful general election campaign led by Lemass
- 1965 - Re-establishes free-trade with Britain
- 1966 – Under Lemass, free Second Level education is introduced
- 1966 – Seán Lemass resigns as Taoiseach and leader of Fianna Fáil
- 1969 – Retires from politics
- 1971 – Seán Lemass dies on 11 May

1960 Presentation of The History of Fianna Fáil to An Taoiseach Seán Lemass at Party HQ.