In 1941, he moved to the Farm Security Administration, where he arranged loans for water facilities and needy farmers in the Mountain states.

Brannan wanted to guarantee farmers income, while letting free market forces determine the prices of commodities.

[citation needed] Following the election of Dwight D. Eisenhower in 1953, Brannan left the government and became the general counsel for the National Farmers Union.

In Mary Robinette Kowal's alternate-history novel The Calculating Stars (2018), Brannan remains secretary of agriculture even after Thomas E. Dewey wins the 1948 presidential election.

He happens to be touring farms in Kansas on March 3, 1952, when a meteorite strike obliterates Washington, D.C.; as the only surviving member of the presidential line of succession, he becomes acting president.