Dennis was born on the 28th of December 1866, in Washington DC, and at the age of 26, he enlisted in the US Army from Pittsburgh, Pennsylvania. Six years later, he was a Private with Troop H of the 10th Cavalry Regiment and was deployed to Cuba in support of the Spanish-American War. It was his actions as part of a landing party from the American steamship named Florida that would earn him the Medal of Honor. The citation reads:

Voluntarily went ashore in the face of the enemy and aided in the rescue of his wounded comrades; this after several previous attempts at rescue had been frustrated.

The Florida had been escorted by a gunboat, the USS Peoria, along with another steamboat names the Fanita. They attempted to land near the port of Cienfuegos, but the area was too heavily defended. The boats landed near the mouth of the Tallabacoa River on the 30th of June 1898, which is when Dennis and the landing party took part in what is now known as the Battle of Tayacoba (due to the American mispronunciation of the river’s name). Dennis and the landing party were the fifth and final attempt to rescue a landing party that had gone ashore to provide reconnaissance on Spanish outpost. They had been discovered and had their boats sank and were stranded until Dennis and four others successfully rescued them during the night. Dennis and three others received their Medals of Honor on the 23rd of June 1899, and Dennis remained in the Army until December of 1903, when he was discharged as a Corporal after eleven years.

Dennis returned to Washington DC where he worked as a mason and on the 25th of September 1953, Dennis Bell died at the age of 86. He is buried in Arlington National Cemetery: Section 31, Grave 349.