Mathias was born in Manchester but moved to Penrhyn-Coch when he was young.
In 1875, he took pastoral charge of Ramah and Erwood, Brecknock and later (in 1881) Llansantffraid and Glyndyfrdwy.
From 1887 he retired to Corwen but resumed the role of pastor in 1893 at Pontlottyn until his death.
Mathias made his breakthrough as a writer while living in Corwen.
He founded, and was editor of, Y Llenor Cymreig published in Corwen between January 1882 and October 1883.