Born in Meriden, Connecticut, Pomeroy received an academic education. He studied and practiced law. He moved to Iowa in 1855, settling in the now-defunct community of Boonesboro, in Boone County. In addition to practicing law, he engaged in agricultural pursuits. An early Republican, in 1860 he was one of the presidential electors for Abraham Lincoln. He served as receiver of the United States land office at Fort Dodge, Iowa, from September 11, 1861, until March 3, 1869, when he resigned to serve in Congress.
In 1868, Pomeroy was elected as a Republican to represent Iowa's 6th congressional district in the U.S. House the Forty-first Congress. The Sixth District then encompassed the northwestern third of the state, extending from the Missouri River as far east as Waterloo and from the Minnesota state line as far south as Marshalltown. In 1870, he was an unsuccessful candidate for renomination, losing to Jackson Orr. In all, he served from March 4, 1869 to March 3, 1871.
He was a claim agent in Washington, D.C. until his death on February 11, 1891. He was interred in Oak Hill Cemetery.