thumb|Portrait of Llewelyn Lewellin
Llewelyn Lewellin (3 August 1798 – 25 November 1878) was a cleric and academic, the first principal of St David's College, Lampeter and the first Dean of St Davids.
Lewellin was born at Tremains, Coity, near Bridgend, Glamorgan, the third son of Richard and Maria Lewellin. He was educated at Cowbridge Grammar School and Jesus College, Oxford, graduating with a BA in 1822, an MA in 1824, a BCL in 1827 and a DCL in 1829. Whilst studying at Oxford, he was ordained deacon in 1822 and priest in 1823 by the bishop of Oxford. In 1826, Lewellin was offered the headmastership of Bruton Grammar School, Somerset. In 1840, he became Dean of St Davids Cathedral, living at St Davids during college vacations.