He was a lawyer before the war.
One of the interesting facts about John Mosby is that before the Civil War, he worked as a lawyer. Mosby made friends with his prosecutor, lawyer William J. Robertson, during his prison term. Robertson gave Mosby use of his legal library when he said he wanted to study law. For the remainder of his sentence, Mosby studied law. Family and friends used their political clout to try to win a pardon. On December 23, 1853, as a Christmas gift, Governor Joseph Johnson pardoned Mosby based on the evidence, and the state legislature later repealed the $500 fee. Mosby was so traumatized by the incident, the court case, and the prison sentence that he never wrote about it in his autobiography.
Before the Civil War, Mosby practiced law. After passing the BAR test, which was necessary to practice law, he started his career in Howardsville in 1855. The community was roughly 25 miles south of Charlottesville, not too far from his house. Mosby met Pauline Clark, the woman he would marry, there. They later have 7 kids together.
John Mosby enlisted in the Confederate forces as soon as the Civil War started. He initially served mostly as a scout, acquiring details about the surroundings and potential adversaries to aid in the impending fights. In the Battle of Bull Run, to speak of battles, he participated in combat.