Known for their distinctive Tiffany-embroidered green flag and Gaelic war cry, "Faugh a Ballagh" (Clear the Way), the Irishmen of the 28th Massachusetts saw action in most of the Union Army's major eastern theatre engagements – Antietam, Fredericksburg, Chancellorsville, Gettysburg, the Overland Campaign, and the siege of Petersburg – and were present for Gen. Robert E. Lee's surrender to Gen. Ulysses S. Grant at Appomattox Court House.
Upon completion of their original three-year term of service, many of the 28th's veteran soldiers elected to return to Massachusetts. But a sufficient number re-enlisted by January 1, 1864, to justify the continuation of the regiment as a five-company battalion of "veteran volunteers" until the end of the war.
For most of its service, the 28th Massachusetts was commanded by Col. Richard Byrnes, who had previously served in the cavalry. Wounded on June 3, 1864, while leading the Irish Brigade at the Battle of Cold Harbor, Byrnes died nine days later.
Stage actor Lawrence Barrett served as captain of the regiment's Company B, but served for less than a year, resigning in August 1862.
Among all Union regiments, the 28th Massachusetts ranked seventh in total losses. Roughly one-quarter of the 1,746 men who served in the unit were killed, died of wounds or disease, taken prisoner, or reported missing.
The surviving veterans of the regiment marched in Washington, D.C., during the Grand Review that celebrated the war's conclusion, then traveled home to Massachusetts, where they were paid and discharged from the service at Readville in June 1865.