[2] Frothingham was a proprietor, and from 1852 to 1865, a managing editor of, The Boston Post.

[2] He was a member of the Massachusetts state legislature in 1839, 1840, 1842, 1849, and 1850, and mayor of Charlestown from 1851 to 1853.

During the 1852 election, Frothingham was an energetic supporter of Franklin Pierce for President.

[4] He devoted much of his time to historical study, and published, in addition to many pamphlets, magazine articles and addresses: For several years, he was treasurer of the Massachusetts Historical Society.

[5] In 1858, Frothingham was elected a member of the American Antiquarian Society.