His father, Robert Campbell, was a Scotsman who served as Chief Factor for the Hudson's Bay Company, the dominant power in the region.
The younger Campbell was educated at Glasgow Academy and the Merchiston Castle School in Edinburgh, and worked as a farmer and rancher upon returning to Canada.
He first campaigned for the Manitoba legislature in the 1892 provincial election as a support of the opposition Conservative Party, and lost to Theodore Arthur Burrows by nine votes in Dauphin.
The Liberal Party won a majority government in this election under Wilfrid Laurier, and Campbell served as an opposition member for the next three years.
When King George V declared war in 1914, Campbell formed Manitoba's 107th Battalion of the Canadian Expeditionary Force which served in France.