Key was a leading attorney in Frederick, Maryland, and Washington, D.C., for many years, with an extensive real estate and trial practice.
He and his family settled in Georgetown in 1805 or 1806, near the new national capital.
He assisted his uncle Philip Barton Key in the sensational conspiracy trial of Aaron Burr and in the expulsion of Senator John Smith of Ohio.
He made the first of his many arguments before the United States Supreme Court in 1807.
In 1808, he assisted President Thomas Jefferson's attorney general in United States v. Peters.

In 1829, Key assisted in the prosecution of Tobias Watkins, former U.S. Treasury auditor under President John Quincy Adams, for misappropriating public funds.
He also handled the Petticoat affair concerning Secretary of War John Eaton, and he served as the attorney for Sam Houston in 1832 during his trial for assaulting Representative William Stanbery of Ohio.
After years as an adviser to President Jackson, Key was nominated by the President to District Attorney for the District of Columbia in 1833.
He served from 1833 to 1841 while also handling his own private legal cases.
In 1835, he prosecuted Richard Lawrence for his attempt to assassinate President Jackson at the top steps of the Capitol, the first attempt to kill an American president.
Key was a leading attorney in Frederick, Maryland, and Washington, D.C., for many years, with an extensive real estate and trial practice. He and his family settled in Georgetown in 1805 or 1806, near the new national capital. He assisted his uncle Philip Barton Key in the sensational conspiracy trial of Aaron Burr and in the expulsion of Senator John Smith of Ohio. He made the first of his many arguments before the United States Supreme Court in 1807. In 1808, he assisted President Thomas Jefferson's attorney general in United States v. Peters.
In 1829, Key assisted in the prosecution of Tobias Watkins, former U.S. Treasury auditor under President John Quincy Adams, for misappropriating public funds. He also handled the Petticoat affair concerning Secretary of War John Eaton, and he served as the attorney for Sam Houston in 1832 during his trial for assaulting Representative William Stanbery of Ohio. After years as an adviser to President Jackson, Key was nominated by the President to District Attorney for the District of Columbia in 1833. He served from 1833 to 1841 while also handling his own private legal cases. In 1835, he prosecuted Richard Lawrence for his attempt to assassinate President Jackson at the top steps of the Capitol, the first attempt to kill an American president.
Francis Scott Key