John G. Chambers was born on September 15, 1828, in Chelsea, Massachusetts, to John and Belinda Chambers. In the early 1840s, he began working at a printing office in Cambridge, Massachusetts. He served in the Mexican American War, and one comrade described him as a “genial comrade and gallant soldier.”
He settled in Boston, Massachusetts, after the war, and he worked as a newspaper typesetter. He married Hannah J. Wilson on October 3, 1852, and they had at least two children: William, born around 1855; and Charles, born around 1857. He moved to Medford, Massachusetts, in the 1850s. By 1860, he owned $1,200 of real estate.
In May 1861, he received a commission as a 1st lieutenant in Company E of the 5th Massachusetts Militia Infantry. The regiment helped defend Washington, D.C., and it took part in the First Battle of Manassas. He mustered out on August 1, 1861.
He returned to the Union army on September 28, 1861, mustering in as an adjutant in the 23rd Massachusetts Infantry. He was promoted to major in March 1862, and he eventually earned a promotion to lieutenant colonel. He was wounded in the side in the Battle of Drewry’s Bluff on May 16, 1864. He died on July 15, 1864, at Fortress Monroe, Virginia.