Stuart, a cousin of Lincoln's future wife, Mary Todd, was impressed with Lincoln and encouraged him to study law. Lincoln was probably familiar with courtrooms from an early age. While the family was still in Kentucky, his father was frequently involved with filing land deeds, serving on juries, and attending sheriff's sales, and later, Lincoln may have been aware of his father's legal issues. When the family moved to Indiana, Lincoln lived within 15 miles (24 km) of three county courthouses. Attracted by the opportunity of hearing a good oral presentation, Lincoln, as did many others on the frontier, attended court sessions as a spectator. The practice continued when he moved to New Salem. Noticing how often lawyers referred to them, Lincoln made a point of reading and studying the Revised Statutes of Indiana, the Declaration of Independence, and the United States Constitution.

Using books borrowed from the law firm of Stuart and Judge Thomas Drummond, Lincoln began to study law in earnest during the first half of 1835. Lincoln did not attend law school, and stated: "I studied with nobody."As part of his training, he read copies of Blackstone's Commentaries, Chitty's Pleadings, Greenleaf's Evidence, and Joseph Story's Equity Jurisprudence. In February 1836 Lincoln stopped working as a surveyor, and in March 1836, took the first step to becoming a practicing attorney when he applied to the clerk of the Sangamon County Court to register as a man of good and moral character. After passing an oral examination by a panel of practicing attorneys, Lincoln received his law license on September 9, 1836. In April 1837 he was enrolled to practice before the Supreme Court of Illinois, and moved to Springfield, where he went into partnership with Stuart.