Lord Rhidian Crichton-Stuart (4 June 1917 – 25 June 1969) was a son of John Crichton-Stuart, 4th Marquess of Bute and Augusta Crichton-Stuart, Marchioness of Bute.
Rhidian Crichton-Stuart was educated at Ampleforth College and at Magdalene College, Cambridge. He gained the rank of Captain in the service of the Royal Artillery (RARO). He was admitted to Royal Company of Archers in 1948. He was British Delegate to the International Legislative Assembly, Tangier between 1953 and 1957. He was a Knight of Obedience, of the Sovereign Military Order of Malta.
He died on 25 June 1969, aged 52.
He married Selina van Wijk on 20 July 1939. They had the following children.
His eldest son, Frederick, also known as Fra' Fredrik Crichton-Stuart, headed Una Voce (Scotland), part of the international body of Una Voce, of which he was president (2005–2006). Una Voce actively promotes and encourages the use of and petitions for wider indults in facilitating the traditional Tridentine Mass in the Catholic liturgy.