Mellen Chamberlain (4 June 1821, Pembroke, New Hampshire - 25 June 1900, Chelsea, Massachusetts) was a United States lawyer, librarian and historian. He was librarian of the Boston Public Library for over a decade.
He graduated from Dartmouth College in 1844 and from the Harvard Law School in 1848. In 1849 he was admitted to the bar, opened a law office in Boston and made his residence in Chelsea, where, during 51 years of citizenship, he served the town in many public capacities. In 1858 and 1859 he was a member of the Massachusetts House of Representatives and the Senate in 1863-64. He was associate justice of the Municipal Court of Boston 1866-70, and chief justice 1870-78.
On 26 August 1878, he was chosen librarian-in-chief of the Boston Public Library, where he served until ill health compelled his retirement in 1890. During his administration, a new library building was begun and the cornerstone laid. Throughout his life he was a close student and investigator of American history.
Besides chapters in Justin Winsor's Memorial History of Boston (1881), he wrote:
- The History of Winnisimmet, Rumney Marsh, and Pullin Point (1880)
- Narrative and Critical History of America (1888)
- John Adams, the Statesman of the Revolution (1884)
- The Authentication of the Declaration of Independence (1885)
- John Adams, the Statesman, with Other Essays and Addresses (1898)
- The Journals of Captain Henry Dearborn, 1775-83 (1886–87)
- The Constitutional Relations of the American Colonies to the English Government at the Commencement of the American Revolution (1887)