In 1806, he was appointed justice of the peace in the London District. In 1812, with Joseph Willcocks, he resisted efforts by Isaac Brock to pass legislation preparing for war with the United States. After Brock dissolved parliament, Mallory was defeated by Mahlon Burwell in the subsequent election.
In 1806, he was appointed justice of the peace in the London District. In 1812, alongside Joseph Willcocks, he opposed Isaac Brock's attempts to pass legislation for war with the United States. Following Brock's dissolution of parliament, Mallory lost his seat in the subsequent election to Mahlon Burwell.