Van Dorn saw action at the Battle of Monterrey on September 21–23, 1846, and during the Siege of Vera Cruz from March 9–29, 1847. He was then transferred to Gen. Winfield Scott's command in early 1847 and promoted to first lieutenant on March 3. Van Dorn fought well in the rest of his engagements in Mexico, earning himself two brevet promotions for conduct; He was appointed a brevet captain on April 18 for his participation at the Battle of Cerro Gordo, and to major on August 20 for his actions near Mexico City, including the Battle of Contreras, the Battle of Churubusco, and at the Belén Gate. Van Dorn was wounded in the foot near Mexico City on September 3, and wounded again during the storming of the Belén Gate on September 13.