Rhiannon Llewellyn was born in Swansea and raised in the UK, USA and France. Rhiannon trained at the RWCMD and the Royal Academy of Music Opera School. Awards include the Maggie Teyte Prize and Miriam Licette Award at the Royal Opera House, Garsington Opera Leonard Ingrams Award, First Prize at the MOCSA Young Welsh Singer Competition, John Kerr Award for Early English Song, AESS Patricia Routledge National English Song Competition and Dunraven Young Welsh Singer Award.

Operatic engagements include Sandman Hänsel und Gretel, Lace Seller Death in Venice, Anna (cover) Intermezzo (all Garsington Opera), Frantik The Cunning Little Vixen, (Glyndebourne Festival Opera), Dalinda Ariodante, Anne Trulove The Rake's Progress, Nella Gianni Schicchi, Erste Dame Die Zauberflöte (cover)(all Royal Academy Opera), Armida Rinaldo (Longborough Festival Opera), Mimì La Bohème (Putney Festival), Cesare Catone in Utica (Dartington), Gala The Shadow of the Wave (Tète-â-Tète Festival), Dalinda (cover) Ariodante (Scottish Opera) and Euridice (cover) in Orfeo & Euridice (English National Opera).

Recital highlights include programmes at The Royal Opera House Crush Room, Madrid's Real Academia de Belles Artes, St. John's Smith Square, Gower Music Festival, Cardiff Music Festival, Gloucester Cathedral, Colston Hall, and in Istanbul. Concert highlights include Serenade to Music under Vladamir Jurowski with Glyndebourne Festival Chorus and the London Philharmonic Orchestra at Royal Festival Hall, a programme of Handel Arias and Duets under Laurence Cummings (Kings Place), Bernstein's Mass under Kristjan Järvi (Royal Albert Hall, BBC Proms), Charlie Barber's Afrodisiac (Purcell Room), Mozart's Requiem under Paul Spicer (St. Martin-in-the-Fields), Orff's Carmina Burana (St. David's Hall), Orff's Carmina Burana under Howard Williams (Colston Hall - National Children's Orchestra of Great Britain), Rossini's Petite Messe Solenelle under Jonathan Wilcocks (Chichester Cathedral), Mahler's 8th Symphony (Bristol Sinfonia), Handel's Messiah (Llandaff Cathedral - Welsh Sinfonia), Bach's St. John Passion (St. Martin-in-the Fields - Choir of Christ College, Cambridge), and Poulenc Gloria (Colston Hall).

In addition to her singing, Rhiannon is a freelance musical director and producer. In a response to the pandemic, Rhiannon set up Putney Music School which now provides music tuition and bursaries to over 100 students and Putney Festival, which presents a dozen performances each year in spaces which range from art galleries, churches and housing estates.