Rockwell was born in Colebrook, Connecticut, and educated at private schools and then Yale, where he studied law, graduating in 1826.

He was elected a member of the Massachusetts House of Representatives in 1834 and served four years, three of them as Speaker.

In 1842 he successfully ran as a Whig candidate for the House of Representatives and was re-elected three times, serving from 1843 to 1851.

He was a delegate to the state constitutional convention in 1853, and was appointed to the Senate in 1854 to fill the vacancy caused by the resignation of Edward Everett, serving from June 3, 1854, to January 31, 1855, when his successor Henry Wilson was elected.

Rockwell voted in the electoral college for the Republican candidate John C. Frémont in the presidential election of 1856.