Major Jackson was admitted to the Pennsylvania Bar in 1788, but in those days, he had to wait two years to practice before the Pennsylvania Supreme Court, the most lucrative branch of the law; besides this, he was an (unpaid) volunteer in the Second Philadelphia Light Horse. He applied to be secretary of the United States Senate, but Samuel Allyne Otis was appointed. He then applied to be personal secretary to George Washington, now first President of the United States, writing that he had unpaid expenses as a Continental officer, and that business was "not congenial to temper."