Evans was born on 1 March 1879 (St David's Day) and educated at St David's College School, Lampeter, Wales.
At Oxford, he obtained first-class degrees in mathematics (1901) and Natural Science (1903).
He was a member of the Indian Educational Service from 1905 to 1922 before being appointed Professor of Mathematics at St David's College, Lampeter (later renamed the University of Wales, Lampeter).
He was High Sheriff of Cardiganshire for the year 1941 to 1942.
[1] Evans was an early member of Plaid Cymru;[2] one of his two sons was the political activist Julian Cayo-Evans.