Carnwath (Gaelic: A' Chathair Nuadh; English: "New Fort") is a moorland village on the southern edge of the Pentland Hills of South Lanarkshire, Scotland. The village lies about 30 mi (50 km) south of both Edinburgh and Glasgow. It is bounded by the North Medwyn and South Medwyn watercourses.

Carnwath stands about a mile north of the old Roman road connecting forts in Tweeddale with those on the Clyde.

The former castle of Carnwath is believed to date to the mid 12th-century built under the orders of William de Sommerville (who died 1160). However, the only remains are the motte which is visible beside the Carnwath Golf Club (founded 1907), at the west end of the village. However, the motte is described as "the most impressive Norman earthwork to survive in Lanarkshire." The motte today is a scheduled ancient monument.

At the centre of Carnwath is Carnwath Cross, the mercat cross, set back a little where the Main Street widens to form the Market Square. This was erected by the 5th Lord Somerville in 1516 to celebrate the granting of burgh status to the village in 1514.

Carnwath collegiate church was established in 1386. The only surviving part of the original collegiate church is St Mary's Aisle, built in 1424 and funded by Thomas Somerville, 1st Lord Somerville (later used as a mausoleum for the Lord Somervilles). St Mary's Aisle is Category A listed. In 1869, a new parish church was built beside the earlier buildings to a design by the Scottish architect David Bryce. The church is Scottish baronial in style and is Category B listed. The church no longer functions as a place of worship.

In 1630, the Carnwath estate, then owned by the Earl of Mar was purchased by Sir Robert Dalzell, later to become Lord Dalzell. In 1639, his son, Robert the 2nd Lord Dalzell, was further elevated to become the Earl of Carnwath. The title was forfeit in 1716 when the 5th Earl of Carnwath, Robert Dalzell was attainted due to his support of the Jacobite cause during the Fifteen, however the titles were restored to the family in 1826. Writer, spy and politician, George Lockhart, inherited the Carnwath estates from his father, Sir George Lockhart, of the Lockharts of Lee, who had purchased them in 1681 from the Earls of Carnwath.

The Ordnance Gazetteer of Scotland (1882–1885) said the village was: "Long a dingy and disagreeable place, it has been greatly improved". In 1845 the area became a civil parish.

Other buildings of note in the village include the old primary school on Main Street, dated 1876 and abandoned since 2006.