Later he served as a British officer in Natchez, Mississippi during the English occupation and was a lawyer, planter, parish sheriff and judge, finally settling at Fairview Plantation on Bayou Sara in Louisiana.

Louisiana had adopted a new constitution in 1845, but the unsettled nature of some of the provisions filled the Johnson Administration with confusion and turmoil; even his inaugural oath was questioned.

In his inaugural speech, Johnson called for moving the state capital from New Orleans to Baton Rouge and stressed the importance of public schools.

Johnson's leadership was a disappointment to state Democratic leaders because he appointed Whigs to office and did not advance strict party disciplines.

By 1848, he had fallen out of favor, and Democrats who supported home-state candidate Zachary Taylor helped carry the state for the Whigs in the 1848 presidential election.