Mathew's political views had moved steadily closer to the Labour Party, and he was selected by the party to fight the Whitechapel and St. George's constituency at the 1922 General Election.[2] At the poll, he defeated the incumbent Liberal MP, James Kiley by just 428 votes.
Mathew died, aged 50, after an operation, less than two months after his election, becoming one of the shortest-serving MPs in history. At the subsequent by-election Harry Gosling held the seat for Labour.