Treharne was born in Glamorganshire, Wales in 1862. In John M. Jenkins 1991 book "Who's Who of Welsh International Rugby Players" his place of birth is stated as Merthyr Tydfil, a fact reiterated by the 1862 birth register. On rugby website Scrum.com, his birthplace is given as Ystradyfodwg, the old parish which once contained what is now the Rhondda. Both facts may be correct as the Merthyr Tydfil registration district during Victorian times contained the parish of Ystradyfodwg. His father, David Treharne, was a land agent in Merthyr. Due to the boom in coal prospecting, David Treharne became wealthy, and later moved to the Rhondda where he built a house in Pentre, called "Pentre House". Edward Treharne was the third child of six, his elder siblings all boys, his younger siblings all girls. Research shows he was the 3rd of six children, two elder brothers, one younger on and two younger sisters.