Gardner was born in Morrow County, Ohio. He entered the Union Army and served in Company D, Sixty-Fifth Regiment, Ohio Volunteer Infantry, from October 1861 to December 1865. He was severely wounded in action at the Battle of Resaca in Resaca, Georgia.
After the war, he attended school at Berea, Ohio, then at Hillsdale College, Hillsdale, Michigan, and graduated from the Ohio Wesleyan University, Delaware, Ohio, in 1870. He studied in the school of theology at Boston University, in 1870 and 1871 and graduated from the Albany Law School in 1876. He was admitted to the bar and commenced practice in Grand Rapids, Michigan. He entered the ministry of the Methodist Episcopal Church, in which he served twelve years. He was commander of the Department of Michigan, Grand Army of the Republic, in 1888. He was professor in Albion College, 1889–1894.
On March 20, 1894, Gardner was appointed Michigan Secretary of State by Governor John T. Rich to fill the vacancy caused by the removal of John W. Jochim. He was then twice elected to the position in 1894 and 1896, serving until 1899. In 1898, he defeated incumbent Democrat Albert M. Todd to be elected as a Republican from Michigan's 3rd congressional district to the 56th United States Congress. He was subsequently re-elected to the five succeeding Congresses, serving from March 4, 1899 to March 3, 1911. He served as chairman of the Committee on Expenditures in the Department of Commerce and Labor in the 61st Congress. He was an unsuccessful candidate for reelection in 1910 to the 62nd Congress.
He was commander in chief of the Grand Army of the Republic in 1913 and 1914. He was an unsuccessful candidate in the primary election for Governor of Michigan. He served as Commissioner of Pensions from March 22, 1921, to March 4, 1925. He retired from public life and died in Albion, Michigan in 1928. He was interred in Riverside Cemetery, in Albion.
Washington Gardner Middle School (formerly Washington Gardner High School) in Albion, Michigan, is named in his honor.
- "Ex-Pensions Chief, Dr. Gardner, Dies. Was Representative From the Third Michigan District for Twelve Years. Former Head of G.A.R. Prominent in the Red Cross and in the Management of Homes for Children". New York Times. April 1, 1928. Retrieved 2010-02-06.
Dr. Washington Gardner, Representative in Congress from the Third Michigan District for twelve years, United States Commissioner of Pensions for ...
- United States Congress. "Washington Gardner (id: G000062)". Biographical Directory of the United States Congress. Retrieved on 2008-02-14
- The Political Graveyard
- Biography at the Grand Army of the Republic
- “The Hon. Washington Gardner”, by Frank Passic, Morning Star, July 4, 1993, p. 19
- History of Calhoun County, Michigan. Vol. 1 and Vol. 2 Washington Gardner, ed. Chicago, New York: The Lewis publishing company, 1913.
John W. Jochim
| Michigan Secretary of State
1896 – 1899
Justus S. Stearns
|U.S. House of Representatives|
Albert M. Todd
| United States Representative for the 3rd Congressional District of Michigan
1899 – 1911
John M. C. Smith