William Pinkney (March 17, 1764-February 25, 1822) was an American statesman and diplomat, and the seventh U.S. Attorney General.
Born in Maryland, Pinkney studied medicine (which he did not practice) and law, becoming a lawyer after his admission to the bar in 1786. After some time practicing law in Harford County, Maryland, he participated in Maryland's state constitutional convention.
Pinkney served in the Maryland House of Delegates from 1788 to 1792 and then again in 1795, and served as a U.S. Congressman from the third district of Maryland in 1791 and from 1815 until 1816. He was mayor of Annapolis from 1795 to 1800, Attorney General of Maryland from 1805 to 1806, co-U.S. Minister to Great Britain (with James Monroe) from 1806 to 1807, and Minister Plenipotentiary from 1808 until 1811. He then returned to Maryland, serving in the Maryland State Senate in 1811, becoming the U.S. Minister Plenipotentiary to Russia, along with a special mission to Naples from 1816 until 1818. In 1811 he joined President James Madison's cabinet as Attorney General.
He was a major in the U.S. Army during the War of 1812 and was wounded at the Battle of Bladensburg, Maryland in August 1814. After the War, he served as Congressman from the fifth district of Maryland from 1815 to 1816, and as a U.S. Senator from Maryland from 1819 until his death in 1822. He is buried at the Congressional Cemetery in Washington, D.C..