He was age 85.
The court announced he died "peacefully" on Thursday, May 8, at his home in Concord, New Hampshire. No cause of death was given.
The Harvard University graduate and Melrose, Massachusetts native joined the high court in 1990 after being nominated by former President George H.W. Bush.
Souter served on the Supreme Court until 2009, when he retired at age 69.
He had served as New Hampshire's attorney general and was a judge on the US Court of Appeals for the First Circuit when Bush nominated him to serve on the Supreme Court.
The first circuit has jurisdiction over Maine, Massachusetts, New Hampshire, Puerto Rico, and Rhode Island.
Click here to follow Daily Voice Greenwich and receive free news updates.