He was the uncle of Director of Public Prosecutions Sir Theobald Mathew and of Irish politician James Dillon.
[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.
[1][3] From 1925, writing under the pseudonym "O", he began to contribute a weekly series of "Forensic Fables" to the Law Journal, which he illustrated himself.
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".