Is US Supreme Court Justice David Souter Jewish?

No, US Supreme Court Justice David Souter is not a Jew. He is an Episcopalian.

According to published reports he plans now to retire from the court.

The religious make-up of the US Supreme Court is as follows:

John Roberts (Chief Justice) - Catholic
Stephen G. Breyer - Jewish
Ruth Bader Ginsburg - Jewish
Anthony M. Kennedy - Catholic
Antonin Scalia - Catholic
David H. Souter - Episcopalian
John Paul Stevens - Protestant
Clarence Thomas - Catholic
Samuel Alito - Catholic

In addition to Ginsburg and Breyer, five previous justices have been Jewish:

Abe Fortas
Arthur J. Goldberg
Benjamin N. Cardozo
Felix Frankfurter
Louis D. Brandeis