Samuel Emerson Smith was born in Hollis, New Hampshire, on March 12, 1788, the seventh child of Manasseh Smith, originally of Leominster, Massachusetts, and Hannah Emerson of Hollis. He attended Groton Academy, and was graduated from Harvard College in 1808. He studied law with Samuel Dana of Groton, Massachusetts, and with his brothers Manasseh and Joseph, and was admitted to the bar in 1812.

Smith entered the practice of law in Wiscasset, Maine, and became interested in politics. He served as a representative to the Massachusetts General Court (1819) and in the Maine legislature (1820-1821). He was appointed chief justice of the Circuit Court of Common Pleas of the Second District (1821) and, upon the reorganization of the court system, became an associate judge of its replacement court (1822-1830).

Smith was elected governor of Maine in 1832. He served three terms and oversaw the move of the state capitol from Portland to Augusta (1832). During his administration issues relating to the controversy over the northeast boundary of the United States (principally the border between Maine and New Brunswick) came to a head. The issue was not settled until 1842, when the current boundary was agreed upon. Soon after leaving office, Smith was reappointed to the Court of Common Pleas (1835) from which he retired in 1837.

While governor, Smith was trustee ex-officio of Bowdoin (1831-1834). He married Louisa Sophia Fuller in 1832 and had nine sons. Smith died at Wiscasset, Maine, on March 3, 1860.