Grant Llewellyn (born 29 December 1960) is a Welsh conductor and music director of the Orchestre National de Bretagne.
There his mentors included Leonard Bernstein, Seiji Ozawa, Kurt Masur and André Previn.
From 2001 to 2006, Llewellyn was the music director of the Handel and Haydn Society (Boston), where he also held the title of principal conductor.
He developed an association with stage director Chen-Shi Zheng with a 2001 production of Henry Purcell's Dido and Aeneas at the Spoleto Festival USA.
Grant Llewellyn is UK President of the Welsh Sinfonia, Wales' professional chamber orchestra, conducted by Mark Eager.