Boomer was born in Sutton, Massachusetts on July 26, 1832. He attended Worcester Academy and graduated in 1847. Because of poor eyesight, Boomer did not go on to college. Instead, he joined his brother-in-law in building bridges across the Mississippi River.
At the outbreak of the Civil War, he raised a company for the Union Army which became part of the 26th Missouri Volunteer Infantry Regiment and by 1863 was promoted to colonel. He distinguished himself at Vicksburg as brigade commander under Major General James B. McPherson.
Boomer and his men distinguished themselves in the Battle of Champion Hill on May 16, 1863. Below is the description of the battle by Benjamin Devor Dean, the second commanding colonel of Boomer's 26th Missouri:
"The 26th went into this engagement under very trying circumstances. General Hovey’s Division was being hard pressed, and falling back, the Third Brigade, Col. Boomer, commanding, was ordered up on the double-quick. The ground over which the 26th Missouri passed, was very much obstructed, and in consequence some of the companies had to break the line of battle and move by the flank under the shells of the enemy. On reaching the line of battle, notwithstanding our fatigue, the 10th Iowa and 93rd Illinois immediately engaged the enemy; the 5th Iowa and 26th Missouri lying down behind them waiting their turn which soon came. Colonel Boomer, our gallant brigade commander, seeing the enemy approaching on our right flank, ordered the 26th Missouri to meet them, which it did on the double quick by "about face," "half wheel" and forward movement, getting possession of a deep ravine which the enemy was trying to secure. The position gained by the above movement was a strong one, and enabled us to stop the enemy who outnumbered the 26th Missouri, which finally drove the Confederates from before it, after firing forty rounds of ammunition. Being nearly surrounded by the enemy, we changed our position under heavy fire, but the position was so strong that the loss was slight considering the hot engagement. We charged the rebels, drove them back and captured a number of prisoners. On falling back to Acting General Boomer’s position, he earnestly complimented the 26th Missouri for their gallant conduct on the field."
Six days after the heroic actions at Champion Hill, Colonel Boomer was killed in the second assault on Vicksburg on May 22, 1863.
According to Benjamin Devor Dean, on May 22 Colonel Boomer led his men on a brave charge upon one of the forts that made up Vicksburg's defenses. Colonel Boomer had advised against storming the fort, warning his superiors that it had not yet been "silenced" of its arms. But his superiors did not listen to his advice, so Colonel Boomer and his men charged the fort gallantly. As Boomer predicted, the fort had not been silenced and immediately he and his men came under heavy fire - "an incessant shower of shot, shell and rifle balls." Colonel Boomer and his men were momentarily forced to take cover. Soon afterwards, Colonel Boomer courageously decided to push on - he personally "rose up, and had shouted "Attention!" as if to resume the charge, when a rifle ball struck him in the head, killing him instantly." Colonel Boomer, who was already an Acting General at the time, had just been commissioned Brigadier General - but he himself would never know this. Reportedly, the commission as Brigadier General arrived in camp shortly after his death.
His body was returned to Worcester, Massachusetts and thousands attended his funeral. He was buried in Rural Cemetery in Worcester and the monument honoring him is a thirty-foot column with a large eagle at the top. His bravery was written about at the time.
A memoir of Colonel Boomer's life was published by his sister, Mary Amelia Boomer Stone, in 1864.