Sean Hales (died 7 December 1922) was an Irish political activist in the early 20th century. Hales was born in Ballinadee, County Cork, where he and his brothers Tom, Donal and Robert (Bob) were involved in the Irish Republican Army (IRA) during the Irish War of Independence.
At the 1921 elections Hales was elected to the Second Dáil as a Sinn Féin member for the Cork Mid, North, South, South East and West constituency. Despite originally being anti-Treaty, Hales was persuaded by Michael Collins to join the pro-Treaty side and he voted for the Treaty.
At the 1922 general election, he was elected to the Third Dáil as a pro-Treaty Sinn Féin Teachta Dála (TD) for the same constituency. Shortly afterwards, the Irish Civil War broke out between the pro-Treaty faction, who were in favour of setting up the Irish Free State and the anti-Treaty faction, who would not accept the abolition of the Irish Republic.
On 6 December 1922, Hales was killed by anti-Treaty IRA men as he left the Dáil. Another TD, Pádraic Ó Máille, was also shot and badly wounded in the incident. His killing was in reprisal for the Free State's execution of anti-treaty prisoners. In revenge for Hales' killing, four republican leaders, whom the Free State held in custody, were executed on 8 December. See also Executions during the Irish Civil War.
According to information passed on to playwright Ulick O'Connor, an anti-Treaty IRA volunteer named Owen Donnelly of Glasnevin was responsible for the killing of Hales. Seán Caffrey, an anti-treaty intelligence officer told O'Connor that Donnelly had not been ordered to shoot Hales specifically but was following the general order issued by Liam Lynch to shoot TDs or senators if they could.