He was named for his maternal grandfather, Captain William Sluman, who had been killed while in command of a private armed vessel during the American Revolutionary War.

Together with other United States citizens, he was interned there, until after the Battle of the Sacramento River in February 1847 he was freed by troops led by Colonel A. W. Doniphan.

After the war ended early in 1848, Messervy ran his business from Santa Fe,[1] now annexed by the US under the U.S. provisional government of New Mexico.

The firm traded in general merchandise with all parts of New Mexico and dealt with natives of the region, as well as with American settlers, and with both the federal and territorial governments.

A young man from Boston, John M. Kingsbury, joined the firm as clerk and book-keeper, and Messervy made trips to the east to buy goods.

These were shipped by rail and canal to Pittsburgh, then by boat on the Ohio, Mississippi, and Missouri rivers to Kansas City, and finally by prairie schooner across the plains to New Mexico.

In 1852–1853, Messervy’s clerk J. M. Kingsbury was also employed as private secretary to the new Governor of the Territory, William Carr Lane.

[17] In April 1854, Messervy, in Santa Fe, wrote to Kingsbury that he would "give a dollar an hour if you and Webb were only here—it would take a great load off my shoulders.

At the end of April 1854, soon after the Battle of Cieneguilla in the war with the Jicarilla, Messervy was superintendent of Indian affairs in New Mexico, as well as acting Governor.

[19] On April 29, 1854, he wrote to the Commissioner of Indian Affairs, George Washington Manypenny:[19] "But as they have commenced this war I am determined unless otherwise instructed from your department to listen to no terms of peace from them… the best interest of this territory and the highest dictates of humanity demand their extinction or their settlement in pueblos.

[18] On July 20, 1854, Messervy resigned as Secretary of the Territory, which also brought to an end his duties as acting Governor,[16][7] and soon after that sold his house on the Santa Fe Plaza to the Kingsburys and Webbs.

[12] Kate Kingsbury decided not to spend her whole time in Santa Fe and also returned to the east, but she continued to make visits to her husband.

[5] In a passport application in March 1841, Messervy was described as born in Salem, twenty-eight years old, five feet four inches in height, with blue eyes, light coloured hair, and a long face and chin.