Trained as a druggist, he achieved notable success in that field, then expanded his energies into banking, transportation and politics.

Though he suffered business reverses during the later 1830s, Henshaw regained his political position as a leader of the Massachusetts Democratic Party within a few years.

In July 1843, President John Tyler selected Henshaw as Secretary of the Navy to follow Abel P. Upshur.

(Gilmer was killed, after only nine days in office, by a canon explosion while firing a salute to a ship passing in review) Henshaw then returned to Massachusetts politics.

After he left this post he dominated Democratic affairs in Massachusetts until the slavery issue began to disrupt parties.