Haf Llewelyn (born June 17, 1964) is a Welsh author and teacher. She has written over 30 books for children and adults.
Llewelyn was born and raised on a mountain farm in Cwm Nantcol, Ardudwy with her four siblings, and she currently lives in Llanuwchllyn, near Bala. She attended Ysgol Gynradd Llanbedr (primary school) and Ysgol Ardudwy (secondary school) in Harlech.
Llewelyn worked as a primary school teacher and on projects with Literature Wales. She won the 2014 Tir na n-Og Award for her book Diffodd y Sêr, about the Welsh poet Hedd Wyn. In 2009, she published Llwybrau, her first volume of poetry and in 2010, she published her first novel for adults, Y Graig. In 2025, Llewlyn served as an adjudicator for the Daniel Owen Memorial Medal at the National Eisteddfod of Wales.