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][3] He took charge of Camp Briggs on September 20 and so impressed the men of 49th Massachusetts with his soldierly bearing and his apparent ease in training them in the manual of arms on one leg that they unanimously elected him colonel.

At that site gathered the various regiments assigned to reinforce the Department of the Gulf in preparation for Major General Nathaniel P. Banks's planned expedition against Port Hudson, Louisiana.

They afterward returned to their camp in Baton Rouge and for the next two months conducted uneventful guard duty in and around the city.

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.

A call was made for 200 volunteers for what was known as a "forlorn hope"—a storming party to lead the division's charge and lay down fascines to allow passage over ditches and trenches.

The 49th Massachusetts reached the foot of the Confederate earthworks gained the most advanced position of any unit in their division that day.

[9] Due to the amputation of his leg and the extremely rugged ground, Col. Bartlett was required to remain on horseback during battle, making him an easy target for Confederates.

[10] During the second assault on Port Hudson, the 49th Massachusetts remained in support, firing on the Confederate position as other units attempted to take the earthworks but failed.

[11] On August 1, 1863, the regiment returned to Baton Rouge and boarded the steamship Temple and traveled up the Mississippi River to Cairo, Illinois.

The total number of deaths consisted of 31 killed in action and mortally wounded and 84 men lost due to disease.