Ifans was born in Haverfordwest, Pembrokeshire, Wales, in 1967, the son of Beti-Wyn (née Davies), a nursery school Teacher, and Eirwyn Evans, a primary school Teacher. He has a brother, actor Llŷr Ifans. Their first language was Welsh. Ifans grew up in Ruthin, Denbighshire, and received his primary education at Ysgol Pentrecelyn. He attended Ysgol Maes Garmon, a Welsh language secondary school in Mold, Flintshire, where he sat his O levels and A levels. He also attended youth acting schools at Theatr Clwyd, Mold, and trained at the Guildhall School of Music and Drama.