South Lanarkshire was a county constituency of the House of Commons of the Parliament of the United Kingdom (Westminster) from 1868 to 1918. It elected one Member of Parliament (MP) by the first past the post voting system.

The Representation of the People (Scotland) Act 1868 provided that the South Lanarkshire constituency was to consist of the parishes of Biggar, Cambusnethan, Carluke, Carmichael, Carnwath, Carstairs, Covington and Thankerton, Crawford, Crawfordjohn, Dalserf, Dolphinton, Douglas, Dunsyre, Lanark, Lesmahagow, Libberton, Pitinain, Shotts, Stonehouse, Walston, Wandell and Lamington, Wiston and Roberton, and so much of the parishes of Culter and Moffat as is situated in the County of Lanark.

The Redistribution of Seats Act 1885 provided that the constituency was to consist of:

the parishes of Biggar, Carluke, Carmichael, Carnwath, Carstairs, Covington and Thankerton, Crawford, Crawfordjohn, Culter, Dolphinton, Douglas, Dunsyre, Lamington and Wandel, Lanark, Lesmahagow, Liberton, Pettinain, Symington, Walston, Wiston and Roberton, Moffat, Avondale, Stonehouse, Glasford, and East Kilbride; so much of the parish of Cathcart as adjoins East Kilbride, and so much of the parish of Kirkpatrick-Juxta as may be in the county of Lanark.