Frothingham was elected a member of the
Massachusetts House of Representatives, and served as Speaker from 1904 to 1905. He was the Republican nominee in the
1905 Boston mayoral election after narrowly defeating former Judge
Henry S. Dewey. He lost the general election to Democrat
John F. Fitzgerald 48% to 39%. He served as the 41st
lieutenant governor 1909–1911, but was an unsuccessful candidate for
governor in 1911. He was lecturer at Harvard. He then moved to
North Easton and continued the practice of law. He was a delegate to the
Republican National Convention in 1916. On May 9, 1916, Frothingham married Mary Shreve Ames in North Easton, Massachusetts. Mary Shreve Ames was a member of the wealthy and prominent Ames family of Easton, Massachusetts, she was the daughter of
Frederick Lothrop Ames the great niece of Congressman
Oakes Ames, and the first cousin, once removed of
Oliver Ames who was Lieutenant Governor and Governor of Massachusetts. Frothingham served as a major in the
United States Army during
World War I. He was a member of the commission to visit the soldiers and sailors from Massachusetts in
France. He served as first vice commander of the Massachusetts branch of the
American Legion in 1919. He was overseer of Harvard University for eighteen years. Frothingham was elected as a
Republican to the Sixty-seventh and to the three succeeding Congresses and served from March 4, 1921, until his death on board the yacht Winsome in
North Haven, Maine on August 23, 1928. His interment was in Village Cemetery in North Easton. ==See also==