He served in the Legislative Assembly of Manitoba as a Conservative from 1899 to 1914, and was a cabinet minister in the governments of Hugh John Macdonald and Rodmond Roblin.

He first ran for the Manitoba legislature in the 1892 provincial election, and lost to Liberal Peter McIntyre by 280 votes in Winnipeg North.

In this period of Canadian history, newly appointed ministers were required to resign their legislative seats to seek a new mandate from their electors.

After Robert Rogers left the provincial legislature for federal politics, Campbell was seen as the second most important minister in Roblin's government.

After unsuccessfully seeking medical care in the United States of America, Europe and Egypt, Campbell returned to Manitoba in summer 1914.