He arrived in Galveston, Texas in 1842 and served under Captain Jesse Billingsley against a Mexican invasion led by General Adrian Woll.

He survived what became known as the Black Bean Episode and was held prisoner for two years before he escaped to Louisiana and returned to Texas.

Walker is said to have self-funded a trip to New York City to meet with Colt and proposed to him the concept of a weapon based on the then-popular five-shot Colt Paterson revolver, with many enhancements such as adding a sixth round, being powerful enough to kill either a man or a horse with a single shot and quicker to reload.

The United States Army's mounted rifle companies were issued them, and they proved extremely effective.

[9] On October 9, 1847, Walker was killed by a rifle bullet while leading a cavalry charge at the Battle of Huamantla.