He was born in Aberdare, the son of 1952 Summer Olympics gold medallist showjumper Sir Harry Llewellyn, 3rd Baronet and the Hon Christine de Saumarez, who was the daughter of the 5th Baron de Saumarez, a family from Guernsey with British naval ties. Llewellyn's middle name, St Vincent, came from his great-grandfather James St Vincent Saumarez, 4th Baron de Saumarez, and originally commemorated the friendship between James Saumarez, 1st Baron de Saumarez and John Jervis, 1st Earl of St Vincent.
Llewellyn grew up at the family homes of Gobion Manor and Llanfair Grange, both near Abergavenny, and was educated at Hawtreys Preparatory School and Eton College. He did not complete his time at Eton, being moved to Milton Abbey School. He then attended Aix-en-Provence University in Southern France and worked as a travel agent, journalist, male model and as the social secretary of the Clermont Club and the Dorcester club.
A supporter of the United Kingdom Independence Party, he stood in the National Assembly for Wales election, 2007, as a candidate for the party in Cardiff North where he came last and polled 3.7% of the vote.
In 1980, Llewellyn married Vanessa Mary Theresa Hubbard, born on 21 February 1958, a niece of the 17th Duke of Norfolk, with whom he had two daughters, actress Olivia Llewellyn (b. 1982) and Arabella (b. 1983). The couple divorced after seven years in 1987, and Vanessa then married John Anstruther-Gough-Calthorpe. In 1999, Llewellyn inherited the Llewellyn Baronetcy upon the death of his father, along with a home in Aberbeeg, near Abertillery.
His younger brother, Roddy Llewellyn is a British landscape gardener and gardening journalist, who was at one time romantically involved with Princess Margaret. Llewellyn's relationship with his brother was soured when he published a lurid account of Roddy's relationship with Princess Margaret. Although Llewellyn later apologised, his brother found it difficult to forgive him, and later made disparaging comments regarding Llewellyn's then fiancée, Christel Jurgenson. The brothers fell out, with many of their comments aired in the tabloid press. In 2008, on the news of Llewellyn's failing health, the brothers finally reconciled.
- Burke's Peerage, vol. 2 (2003), p. 2370
- "Sir Dai Llewellyn, Bt: playboy and bon vivant". The Times (London). 2009-01-15. Retrieved 2009-01-17.
- Sir Dai says: Wales, vote for me - icWales
- Llewellyn, Dai (13 September 2008). "Doctors told man-about-town Dai Llewellyn give up the drink or die". Daily Mail. Retrieved 26 May 2015.
- "Sir Dai Llewellyn". The Daily Telegraph (London). 14 January 2009.
- Burgess, Kaya (14 January 2009). "Sir Dai Llewellyn dies aged 62". The Times (London). Retrieved 14 January 2009.
- Kay, Richard (22 January 2009). "Sarah Ferguson joins Dai Llewellyn's grieving daughters at funeral of famed bon viveur". Daily Mail. Retrieved 26 May 2015.
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|Llewellyn Baronets of Bwlffa