Brice left the Army in 1832 and moved to Ohio. He passed the bar exam, began to practice law, and in 1846 was elected an associate judge of the court of Licking County, Ohio. Later in 1846, Brice was appointed Adjutant General of the state militia by Governor William Bebb and served until 1847, when he resigned to re-enter the army to serve in the Mexican War. Brice became United States Army Paymaster under President James K. Polk at the rank of major and served from March 3, 1847, to March 4, 1849. He saw service at Camargo in 1847, Monterrey, Saltillo, and Brazos Island in 1848, and was then stationed at Fort Brown, Texas, from 1848 to 1849.