Carnedd Llewelyn, usually spelt Carnedd Llywelyn in Welsh, is a mountain massif in the Carneddau range in Snowdonia, north-west Wales. It is the highest point of the Carneddau and the second highest peak by relative height in Wales, and lies on the border between Gwynedd and Conwy.
Carnedd Llewelyn lies in the middle of the main north-east to south-west ridge of the Carneddau, between Carnedd Dafydd to the south-west and Foel Grach to the north. A short subsidiary ridge links it to Yr Elen to the north-west. Its position means that any route to this summit involves a long walk. It can be climbed from Gerlan, above Bethesda, taking the path following Afon Llafar then continuing to the summit of Yr Elen before following the short ridge to Carnedd Llewelyn.