William Watson, Baron Thankerton, PC (8 December 1873 – 13 June 1948), was a Scottish Unionist Party politician and judge.

Born in Edinburgh, Watson was the third son of Margaret Bannatyne (1846–1898) and William Watson, Baron Watson (1827–1899). He was educated at Winchester College and Jesus College, Cambridge, graduating with a Third in Law in 1895.^[1] In 1899, he was admitted to the Faculty of Advocates,^[2] taking silk in 1914.^[3] He was Procurator to the General Assembly of the Church of Scotland from 1918 to 1922, and was an advocate depute in 1919.

Watson was the Member of Parliament for Lanark South from 1913 to 1918^[4] and for Carlisle from 1924 to 1929.^[5] He held office as Solicitor General for Scotland from July 1922^[6] to November 1922, and as Lord Advocate from November 1922^[7] to February 1924 and from November 1924^[8] to May 1929. He was appointed a Privy Counsellor in 1922. He was raised to the bench as a Lord of Appeal in Ordinary and created a life peer as Baron Thankerton, of Thankerton in the County of Lanark, on 1 May 1929,^[9] holding the post until his death at 74 in 1948.

Lord Thankerton's hobby was knitting, and he would practise this while hearing cases.^[10]