Lyman Tremain was born on June 14, 1819, in Durham, Greene County, New York. He was educated at the local common school and entered the Kinderhook Academy at the age of 13. Tremain commenced his legal studies in the Durham law office of John O'Brien, and later studied in the law firm of Sherwood & White in New York City. In 1840, he was admitted to practice, returned to Durham, and became a partner in the O’Brien law office. Four years later, Tremain was appointed District Attorney of Greene County and, following the adoption of the Constitution of 1846, was elected County Judge and Surrogate of Greene County. At the expiration of his term of office, he was not reelected. Tremain ran as the Republican candidate for Lieutenant Governor of New York in 1862, but lost the election and moved to Albany where, in 1853, he formed a law partnership with Rufus W. Peckham.
Lyman Tremain was elected Attorney General of New York on the Democratic ticket in 1858 and held office for two years. In 1866, he was elected to a two-year term in the New York State Assembly, and served as Speaker in 1867.
During his highly successful legal career, many times the State of New York selected Tremain to prosecute capital and other serious cases. In 1867, Lyman served as one of the three prosecutors in the trial of Major General George W. Cole, accused of murdering Assemblyman L. Harris Hiscock. Cole believed that Hiscock had had an affair with Mrs. Cole while the general was serving with the army. His first trial ended with a hung jury, and he was acquitted at the second on the grounds of "momentary insanity."
Another famous trial occurred in 1871, when Boss Tweed was arrested and charged with embezzlement of public funds. The prosecution team consisted of Wheeler H. Peckham, Benjamin K. Phelps and Lyman Tremain. The jury found Tweed guilty on November 19, 1873.
Tremain also served as defense counsel, and was perhaps most famous for his representation of Edward S. Stokes, accused of killing financier "Diamond Jim" Fisk in 1872. Fisk and Stokes were rivals for the affections of the voluptuous beauty, Josie Mansfield. Stokes was charged with murder in the first degree, but his counsel secured a manslaughter verdict and Stokes was sentenced to State prison for four years.
Lyman Tremain was elected as a Republican to the Forty-third Congress (March 4, 1873 – March 3, 1875). At the end of his term, he returned to his law practice in Albany and died on November 30, 1878 while visiting New York City. He is buried in the Rural Cemetery, Albany, New York.
Tremain's son, Frederick Lyman (June 1843 – February 6, 1865), was a lieutenant colonel of the 10th New York Cavalry during the Civil War and was killed at the Battle of Hatcher's Run.
George Rogers Howell, Jonathan Tenney. Bicentennial History of Albany: History of the County of Albany, N. Y., from 1609 to 1886, Volume 4 (1886).
The American Government: Biographies of members of the House of Representatives of the Forty-third Congress (1874). Biographical Guide to Congress.