Beal studied at the Westbrook Seminary and was very interested military affairs, eventually being elected captain of the local militia unit known as the Norway Light Infantry, a position he held at the beginning of the war.

He received a brevet promotion to brigadier general of U. S. Volunteers on August 22, 1864, and was replaced as commander of the 29th Maine by Colonel George H. Nye on October 4, 1864.

For gallant service at the Battle of Cedar Creek, he was promoted to full brigadier general of U. S. Volunteers November 30, 1864.

Following the war, he was breveted to major general (on or retroactive to March 13, 1865) and assigned command of the eastern district of South Carolina during the Reconstruction era.

He also served as commander of the Maine Commandery of the Military Order of the Loyal Legion of the United States.