He studied law, was admitted to the bar in 1880 and commenced practice in Houlton.

He was chairman of the U.S. House Committee on Expenditures on Public Buildings in the Sixty-sixth Congress, and was one of the managers appointed by the House of Representatives in 1926 to conduct the impeachment proceedings against George W. English, judge of the United States District Court for the Eastern District of Illinois.

He became judge of probate for Aroostook County, Maine, serving from 1934 until 1942, when he retired and moved to Washington, D.C.

He died on May 6, 1943, in Washington and he was buried in Evergreen Cemetery in Houlton, Maine.

Hersey supported the Immigration Act of 1924, saying during a speech in the House of Representatives the United States was "a mighty land settled by Northern Europeans from the United Kingdom, the Norsemen, and the Saxon.