Williams has been the rumored front-runner for the past week, although Nationals bench coach Randy Knorr and third base coach Trent Jewett reportedly received strong consideration.
Washington will attempt to keep Knorr as the bench coach under Williams according to Rosenthal. Knorr informed Adam Kilgore of the Washington Post that he is open to staying, telling the reporter "I love this team."
The Arizona Diamondbacks have employed Williams on their coaching staff for the past four seasons. Williams served as the first base coach in 2010, then moved to third base coach from 2011-2013.
Nationals general manager Mike Rizzo knows Williams from his playing career. Rizzo served as the Diamondbacks' scouting director when Williams manned third base in Arizona. Williams played 16 seasons in the majors, making five All-Star teams and winning a World Series with the 2001 Diamondbacks.
Williams has little previous managing experience. He served as an interim manager for the Diamondbacks Double-A team for two months in 2007, and managed the Salt River Rafters in the Arizona Fall League last year.