He was the uncle of Director of Public Prosecutions Sir Theobald Mathew and of Irish politician James Dillon.
Mathew was educated at The Oratory School and Trinity College, Oxford, where he obtained second-class honours in History in 1888.
[1] Like his father and brother, he was called to the bar at Lincoln's Inn in 1890, and practiced in the chambers of Joseph Walton, later a High Court judge.
[1] Mathew had a large practice at the common law bar; after the First World War he frequently appeared in Canadian appeals to the Judicial Committee of the Privy Council.
On one occasion, Mathew, upon meeting a white friend in the library of an Inn of Court which had many African members, greeted him with "Dr. Livingstone, I presume", a remark which was said to have "acquired legendary status during his lifetime".