Gilman Marston (August 20, 1811 - July 3, 1890) was a United States Representative, Senator, and United States Army general from New Hampshire. Born in Oxford, New Hampshire, he graduated from Dartmouth College in 1837 and from the law department of Harvard University in 1840. He was admitted to the bar and commenced practice in Exeter, New Hampshire in 1841 and was a member of the New Hampshire House of Representatives from 1845 to 1849. He was a delegate to the State constitutional convention of 1850.
Marston was elected as a Republican to the Thirty-sixth and Thirty-seventh Congresses (March 4, 1859-March 3, 1863). He served in the Union Army during the Civil War, resigning his commission as brigadier general in 1865. He was elected to the Thirty-ninth Congress (March 4, 1865-March 3, 1867) and in 1870 declined the Governorship of Idaho Territory. In 1872, 1873, and 1876 to 1878, he was again a member of the State house of representatives. He was an unsuccessful candidate for election in 1876 to the Forty-fifth Congress and was a delegate to the State constitutional convention of 1876.
On March 4, 1889, Marston was appointed to the U.S. Senate to fill the vacancy in the term commencing on that date and served until June 18, 1889, when a successor was elected. He died in Exeter in 1890; interment was in Exeter Cemetery.