William Pinkney was born in Annapolis, Maryland, in 1764, and while he received no formal college education, many considered him the finest American lawyer of his era. Pinkney gained his first political experience as a member of the Maryland House of Delegates (1789-1792), a seat he earned following his participation in the Maryland constitutional convention of 1788. After a brief and contested stay as a United States representative in 1791, he returned to Maryland, serving on the state executive council (1792-1795) and again with the House of Delegates (1795). His domestic political career continued in 1805 with his service as Maryland's attorney general. In 1811, he rose to the position of U.S. attorney general in the cabinet of President James Madison, where he served until 1814. While attorney general, Pinkney also participated in the War of 1812, serving as a major in the Maryland militia.

He went on to served the United States in several capacities overseas as well, including joint minister to Great Britain (1806-1807); minister plenipotentiary to Great Britain (1807-1811); and minister plenipotentiary to Russia and Naples (1816-1818). Pinkney returned to the United States in 1819 to serve a final term with the U.S. Senate and died in Washington, D.C., while in office, on February 25, 1822.