In November 1846, he was enrolled in Philadelphia as a Captain in command of Company G, First Pennsylvania Regiment, known as the "Jefferson Guards". He took an active part through to the end of the war in Scott's Mexico City Campaign, principally the engagements of the Siege of Veracruz, National Bridge, Cerro Gordo, Castle Perote, Huamantla, and the Siege of Puebla. Discharged July 29, 1848, Morehead returned to Philadelphia, but soon began his participation in the "Philadelphia Blues" Battalion.