Upon the outbreak of the Mexican–American War, Locke enlisted in the 1st Regiment of Mississippi Volunteers, where he was a bodyguard to Col. Jefferson Davis.
When Taylor resigned on 18 January 1858, Locke was elected Speaker over Reps. Isaac N. Dennis and John Henry Brown, 39 votes to 14 and 13, respectively.
Edward Clark, he resigned his senate seat and raised the unit that became the 10th Texas Cavalry Regiment when it was transferred to the Confederate Army.
After the war, Locke settled in Arkansas and was one of the founders of the town of Alma, where he married Narcissa A. Montgomery.
His residence, the first in Alma, was constructed in 1868–1869 using lumber hauled in by oxen team, and was located at the corner of Fayetteville Road and Walnut Street.