John Joseph (Sean) Liddy (1890–1965) was an Irish politician and founder member of the Garda Síochána (the police force of the Republic of Ireland). On his retirement, he also founded and became the first President of the Garda Pensioners Association (1961–1966), later to be renamed the Garda Síochána Retired Members Association (GSRMA).
Alongside lifelong friend Michael Collins, he was a prominent veteran of the Irish War of Independence. Subsequently, he served as a Teachta Dála (TD), Army Officer and Garda Chief Superintendent.
In the 1921 elections, he was elected unopposed to the 2nd Dáil as a Sinn Féin TD for the constituency of Clare. He supported the Anglo-Irish Treaty and voted in favour of it. He was re-elected unopposed as a pro-Treaty Sinn Féin TD at the 1922 general election. He resigned as a TD on 18 December 1922.
He died as a result of a motor accident in March 1965.
The Liddy Medal – the Garda Veterans Injury Award – is named in his memory. The medal is presented to retired Gardaí who were injured in the line of duty while in the force.