He studied at Eastman Business College in Poughkeepsie, New York and later at the Coburn Classical Institute in Waterville, Maine.

After graduating he engaged in the agriculture business, including ventures in lumber, lime, and creameries in Rockland and cattle raising elsewhere.

In 1908, he launched an unsuccessful campaign to become governor, losing to Republican candidate Bert M. Fernald.

During this time, Gardner served in the Senate with fellow Democrat Charles Fletcher Johnson.

Following this defeat, he was appointed a member of the International Joint Commission created to prevent disputes between Canada and the United States over shared boundary waters.