The 3rd Massachusetts Volunteer Heavy Artillery Regiment was a unit that served in the Union Army during the American Civil War.

It was organized from already mustered unattached companies of heavy artillery raised for the defenses of the Massachusetts coast.

Beginning in January 1863, and continuing until early 1864, twelve companies of heavy artillery were raised in Massachusetts and mustered into service to garrison the military forts along the coast of the state.

In the spring of 1864, the 3rd Unattached Company, along with the 6th through 12th, were ordered to Washington, DC, where they were to garrison the forts protecting the capital.

Because of their engineering skills, they were detached from the regiment and attached to the Army of the James, and were engaged in building bridges and roads.