South Tyrone was a UK Parliament constituency in Ireland which returned one Member of Parliament from 1885 to 1922, using the first past the post electoral system.
From 1801 to 1885, County Tyrone returned two MPs to the House of Commons of the United Kingdom sitting at the Palace of Westminster, with separate representation for the parliamentary borough of Dungannon. Under the Redistribution of Seats Act 1885, Dungannon ceased to exist as a parliamentary borough and the parliamentary county was divided into four divisions: North Tyrone, Mid Tyrone, East Tyrone and South Tyrone.
Under the Redistribution of Seats (Ireland) Act 1918, following a boundary commission review, the parliamentary county lost a seat, leading to an expansion of the territory of South Tyrone. Sinn Féin contested the 1918 general election on an abstentionist platform in its election manifesto pledging that instead of taking up any seats at Westminster, they would establish an assembly in Dublin. All MPs elected to Irish seats were invited to participate in the First Dáil convened in January 1919, but no members outside of Sinn Féin did so, with South Tyrone's William Coote listed on the roll as "" [absent].
The Government of Ireland Act 1920 established the Parliament of Northern Ireland, which came into operation in 1921. The representation of Northern Ireland in the Parliament of the United Kingdom was reduced from 30 MPs to 13 MPs, taking effect at the 1922 United Kingdom general election. At Westminster, the three divisions of County Tyrone and the two divisions of County Fermanangh were replaced by a two-member county constituency of Fermanagh and Tyrone. An eight-seat constituency of Fermanagh and Tyrone was created for the House of Commons of Northern Ireland, which formed the basis in republican theory for representation in the Second Dáil after the 1921 election. Three Sinn Féin representatives sat as TDs for the constituency, two of whom also represented constituencies in Southern Ireland.