William Pinkney (March 17, 1764 – February 25, 1822) was an American statesman and diplomat, and was appointed the seventh U.S. attorney general by President James Madison.

William Pinkney was born in 1764 in Annapolis in the Province of Maryland. His parents' home was on the banks of the Severn River, from where the family could see the Chesapeake Bay. He had English ancestry.

Pinkney attended the private King William school. His teacher was a Mr. Brefhard. Although Pinkney left school at the age of thirteen, he had impressed his teacher with his intelligence, and Brefhard agreed to give the youth private lessons at home.

Pinkney studied medicine (which he did not practice) and "read the law" with an established firm, as was the practice at the time for aspiring lawyers. He was admitted to the bar in 1786. After practicing law for two years in Harford County, Maryland, Pinkney was elected as a delegate to Maryland's state constitutional convention.

Pinkney was an excellent orator who possessed an impressive command of language. He was said to have been articulate and pleasing in manner.

After beginning his law practice, he married Anne Rodgers. They had ten children together. Edward Coote Pinkney, born seventh, was ranked as an accomplished poet posthumously.

In April 1788, Pinkney was elected a delegate to the convention of the State of Maryland, which ratified the United States Constitution. This marked the beginning of his political career.

Pinkney served in numerous electoral offices, at the local, state and national level. He was elected to and served in the Maryland House of Delegates from 1788 to 1792 and then again in 1795. He was elected mayor of Annapolis, serving from 1795 to 1800.