Joseph Bradley Varnum (January 29, 1751–September 21, 1821) was a U.S. politician of the Democratic-Republican Party from the state of Massachusetts.

Varnum was born in Dracut, Massachusetts. He was a farmer who, despite having little formal education, was learned enough to serve as a justice of the court of common pleas and a chief justice of the court of general sessions.

After serving in the American forces during the American Revolution, Varnum served for 15 years in the Massachusetts state legislature, starting in the House of Representatives (1780–1785) before moving up to the Senate (1786–1795).

In 1795, Varnum was elected to the U.S. House of Representatives, where he served from March 4, 1795 until his resignation on June 29, 1811. During his last four years in the House, he served as its Speaker.

Varnum was elected to the U.S. Senate in 1811 for one term; after returning to Massachusetts in 1817, he again served in the state Senate, until his death.

Varnum died in Dracut, and his body is interred in Varnum Cemetery.