John Nelson was an American lawyer and statesman who served as the Attorney General of the United States from 1843 to 1845 under President John Tyler. He served as the first United States Chargé d'Affaires to the Kingdom of the Two Sicilies from 1831 to 1832 and as the U.S. representative for Maryland's 4th district from 1821 to 1823.

The United States attorney general (AG) is the head of the United States Department of Justice, and is the chief law enforcement officer of the federal government of the United States. The attorney general serves as the principal advisor to the president of the United States on all legal matters. The attorney general is a statutory member of the Cabinet of the United States.