After leaving provincial politics, Stewart was invited to join the federal cabinet of William Lyon Mackenzie King, in which he served as Minister of the Interior and Mines. In this capacity he signed, on behalf of the federal government, an agreement that transferred control of Alberta's natural resources from Ottawa to the provincial government—a concession he had been criticized for being unable to negotiate as Premier. He served in King's cabinet until 1930, when the King government was defeated; in the 1935 election, Stewart lost his seat in the Alberta Legislative Assembly. He died in December 1946 in Ottawa.
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