Grant served in the Mexican-American War beginning in 1846. He served under two eminent generals—Zachary Taylor and Winfield Scott. Grant followed in the footsteps of these two leaders in becoming a presidential candidate. Taylor served as the nation’s twelfth president, while Scott lost the presidential election of 1852 to Franklin Pierce. Grant earned a promotion to second lieutenant during the Mexican–American War.

Grant served as quartermaster of the Fourth Infantry while a twenty-four-year-old lieutenant. He proved himself well, earning the respect of his fellow officers and soldiers.