Middlesex East was a federal electoral district in Ontario, Canada, that was represented in the Canadian House of Commons from 1867 to 1968. It was created by the British North America Act of 1867, which divided the County of Middlesex into three ridings: Middlesex North, Middlesex West and Middlesex East.
In 1882, the East Riding of the county of Middlesex it was defined as consisting of the townships of London, West Nissouri, North Dorchester and South Dorchester, the town of London East and the villages of London West and Springfield.
In 1903, the east riding was defined to consist of the townships of Dorchester North, London, Nissouri West and Westminster.
In 1914, the county of Middlesex was divided into two ridings, Middlesex East and Middlesex West. The east riding consisted of the townships of Dorchester North, London, Nissouri West, Westminster and Biddulph, the village of Lucan and those portions of the city of London not included in London city riding.
In 1924, it was redefined to consist of the part of the county of Middlesex lying east of and including the townships of Biddulph, London and Westminster, and those portions of the city of London not included in London city riding.
In 1947, it was redefined to consist of the townships of North Dorchester, London, West Nissouri and Westminster, and the eastern part of the City of London.