Port Arthur was a federal electoral district represented in the House of Commons of Canada from 1935 to 1979.

It consisted initially of the parts of the territorial districts of Algoma, Cochrane, Kenora, and Thunder Bay not included in the electoral districts of Algoma West, Cochrane, Fort William, and Kenora-Rainy River herein defined, and including the city of Port Arthur, together with that part of the district of Patricia not included in the electoral districts of Kenora—Rainy River and Cochrane.

In 1966, it was defined as consisting of the part of the territorial district of Thunder Bay contained in the City of Port Arthur and the Townships of Adrian, Blackwell, Conmee, Forbes, Fowler, Goldie, Gorham, Horne, Jacques, Laurie, MacGregor, McIntyre, McTavish, Oliver, Sackville, Sibley and Ware.

The electoral district was abolished in 1976 when it was merged into Thunder Bay—Nipigon riding.

Port Arthur has elected the following members of Parliament: