Philip Barton Key (April 12, 1757 – July 28, 1815) was a Representative from the third district of Maryland. Unusually for a politician in the early United States, Key had been a Loyalist in the American Revolution.
Born in Charleston, Cecil County, Maryland, Key pursued an academic course. During the War of Independence he served in the Maryland Loyalists Battalion as a captain. He was captured by the Spanish in Florida with the rest of his battalion. He was kept as prisoner for a month in Havana, Cuba, before being paroled and sent to New York City until the end of the war.
After the war Key traveled to England to study law at the Middle Temple. In 1785 he returned to Maryland was admitted to the bar. He began practising law in Leonardtown, Maryland before moving to Annapolis in 1790, becoming a member of the Maryland House of Delegates from 1794 until 1799. He served as Mayor of Annapolis from 1797 to 1798. On February 25, 1801, he was nominated to the Fourth United States Circuit Court.
In the fall of 1806 Key moved to Montgomery County, Maryland and became interested in agriculture. Between March 4, 1807 and March 3, 1813, he was elected as a Federalist to the Tenth, Eleventh and Twelfth U.S. Congresses. He also served as chairman for the Committee on District of Columbia during the Tenth Congress.