Served as an associate justice of the U.S. Supreme Court from 1792 to 1793.
He was admitted to the bar in Maryland in 1753 and served as the first governor of Maryland.
His legacy was honored with several academic institutions being named after him: Governor Thomas Johnson High School in Frederick, Maryland, Governor Thomas Johnson Middle School in Frederick, Maryland, Thomas Johnson Middle School in Lanham, Maryland, and Thomas Johnson Elementary School in Baltimore, Maryland.
He married Ann Jennings in 1766. They had eight children together.
He was nominated to the Supreme Court by President George Washington.