Sir Rhys Rhys-Williams, 1st Baronet DSO QC DL (20 October 1865 – 29 January 1955), born Rhys Williams, was a British Liberal Party politician from Wales. He later left the Liberal Party for the Conservatives.
Rhys-Williams was the son of Judge Gwilym Williams and Emma Eleanor Williams JP. His wife Juliet Rhys-Williams (née Glyn) was a writer and prominent Liberal politician who, like her husband, later joined the Conservative Party via the Liberal Nationals. They met in 1919 when Juliet Glyn began working for Rhys-Williams as his private secretary during his period of office as parliamentary secretary at the Ministry of Transport. They married on 24 February 1921 They had two sons and two daughters. Their son, Sir Brandon Rhys-Williams became a Conservative MP and Member of the European Parliament.
Rhys-Williams was educated at Eton College, which he entered in 1880, and Oriel College, Oxford.
In the First World War he served in the Welsh Guards, reaching the rank of Lieutenant-Colonel. He saw active service, was wounded, was twice mentioned in despatches and won the DSO. In 1915 he served for a year as Acting Military Attaché at the British Legation in Tehran. He ran an intelligence service for the Russians in their campaigns against the Turks and was awarded the Order of St. Vladimir with the Swords by the Czar in 1916. In 1917 Rhys-Williams was attached the War Office to act as Assistant Director-General Movements and Railways.