Serving on Lake Ontario during the War of 1812, he later cruised off Africa and South America, in the West Indies and in the Pacific.

While in command of the Savannah during the war with Mexico, 1846 and 1847, he led a detachment of sailors and United States Marines against Monterey, California, and on 7 July 1846, took possession and hoisted the American flag over the city.

On 7–9 October 1846, Mervine led 203 U.S. Marines, 147 American sailors, and volunteers in the invasion of Los Angeles where he lost the Battle of Dominguez Rancho.

However on 22 September 1861, he was removed as commander of the blockade force by Secretary of the Navy Gideon Welles.

He stated he found it "difficult to understand the reasons for the apparent inactivity and indifference that have governed in this matter.