Just after his thirteenth birthday in 1815, Pinkney joined the United States Navy as a midshipman until 1824, during which time he traveled to Italy, northern Africa, the West Indies, and both coasts of South America. His defiance of what he called arbitrary authority got him in trouble occasionally. In 1824, two years after the death of his father, he left the Navy, married, and was admitted to the bar in Maryland. Though he was well respected in his abilities as a lawyer, he had few clients and the business failed. His wife, Georgiana McCausland, would become a supportive and inspirational figure to him.