Obadiah Gardner (September 13, 1852 - July 24, 1938) was an American politician from the U.S. state of Maine. Gardner was a businessman and member of the Democratic Party who served in several minor state executive positions before serving a single six-year term in the United States Senate.
Gardner was born near Port Huron, Michigan. In 1864 he moved with his parents to Union, Maine, where he attended public schools. He studied at Eastman's 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.
He was a member of the Maine Board of Agriculture and later the master of the Maine State Grange (1897-1907). In 1908, he launched an unsuccessful campaign to become Governor, losing to Republican candidate Bert M. Fernald. In 1911, he was appointed as chairman of the Board of State Assessors, but resigned after being appointed and later elected Senator, filing the vacancy caused by the death of William P. Frye. Gardner served from September 23, 1911, until March 3, 1913, when he lost his bid for re-election. 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. Later he became chairman of the American delegation, serving until his retirement in 1923.
Gardner returned to Rockland and later moved to Augusta, where he died. He is interred in the Achorn Cemetery in Rockland.