It was one of the 18 Massachusetts regiments formed in response to President Abraham Lincoln's August 1862 call for 300,000 men to serve for nine months.

[2] Colonel Eben F. Stone, a prominent lawyer from Newburyport, Massachusetts, commanded the regiment.

Lieutenant Colonel James O'Brien of Charlestown, Massachusetts, who was originally to command the intended Irish regiment, served as second-in-command.

Their first field duty consisted of a reconnaissance towards Port Hudson with other units of the IX Corps from March 13–20.

[2][3] They remained at Camp Banks for two months serving uneventful duty as planning for the expedition against Port Hudson encountered logistical delays.

The regiment saw its first combat before the day was out as Union forces just outside of Baton Rouge encountered a Confederate column from Port Hudson precipitating the Battle of Plains Store.

[7] O'Brien was shot and killed as he led the "Forlorn Hope" and exposed himself to severe fire largely in an effort to redeem himself and the regiment for his error in allowing the enemy to outflank them at Plains Store.

[6] As Union forces settled in for a siege, the 48th Massachusetts returned to Baton Rouge for a short time to serve guard duty.

Many in the regiment suffered from disease at this time and when they were summoned back to Port Hudson, many were in a weakened state.

The total number of deaths consisted of 19 killed in action and mortally wounded and 50 men lost due to disease.