When the Mexican War broke out, Butler again joined the army.
On June 29, 1846, he was appointed major general of volunteers and commanded the 1st Volunteer Division in the Army of Occupation.
 He served as second-in-command to Zachary Taylor during the Battle of Monterrey, in which he was wounded.
 On February 18, 1848, he superseded General Winfield Scott as the commanding general of the American army in Mexico City.
 He left the service on August 18, 1848, after he had been selected as the Democratic Vice Presidential nominee.
When the Mexican War broke out, Butler again joined the army. On June 29, 1846, he was appointed major general of volunteers and commanded the 1st Volunteer Division in the Army of Occupation.  He served as second-in-command to Zachary Taylor during the Battle of Monterrey, in which he was wounded.  On February 18, 1848, he superseded General Winfield Scott as the commanding general of the American army in Mexico City.  He left the service on August 18, 1848, after he had been selected as the Democratic Vice Presidential nominee.
William Orlando Butler