Carnedd Dafydd is a mountain peak in the Carneddau range in Snowdonia, north Wales, and is the third highest peak in Wales, or the fourth if Crib y Ddysgl on the Snowdon ridge is counted. Situated south-west of Carnedd Llewelyn and north of Pen yr Ole Wen, Carnedd Dafydd is on the main ridge of the Carneddau, and on the border between Gwynedd and Conwy.
Carnedd Dafydd is usually climbed by first ascending Pen yr Ole Wen and then following the ridge along to Carnedd Dafydd, though it is also possible to make a direct ascent from Tal y Llyn Ogwen, first following the stream, Afon Lloer, to the mountain lake of Ffynnon Lloer then climbing up the slope to the summit.
Like most of the summits in the southern Carneddau, it has a flat, boulder-strewn summit plateau. Immediately to the north lie the crags of Ysgolion Duon, well-known to climbers.
The origin of its name, which translates as Dafydd's (or David's) cairn, like that of its neighbouring peak, Carnedd Llewelyn (Llywelyn's cairn), is the subject of some confusion. One possibility is that they are named after Llywelyn ap Gruffudd, the last independent prince of Wales, and his younger brother, Dafydd ap Gruffudd. A second possibility is that they are named after Llywelyn the Great, an earlier prince of Gwynedd, and his son and successor, Dafydd ap Llywelyn. Other sources cite a combination of these options, e.g. Llywelyn the Great and Dafydd ap Gruffydd.