King, who was an intern under Washington running backs coach Randy Jordan during the 2020 season, is the second female assistant coach in the NFL after Tampa Bay Buccaneers assistant defensive line coach Lori Locust.
Washington head coach Ron Rivera said King deserved the promotion for the hours she put in for in-season and off-season work in a season where they made the playoffs.
"She demonstrated all of the qualities that are needed to work full-time on my staff," Rivera said in a statement.
"She is a hard worker, a great communicator and a quality person. Coach King is always eager to learn and has shown tremendous growth since starting here last season.
"I know she will continue to be an asset... She earned this opportunity with her hard work. The sky is truly the limit for her."
King, a seven-times All-American quarterback and wide receiver for the Carolina Phoenix women's tackle football team from 2006-17, also has experience as a coach in women's basketball.
She was the head coach of Johnson & Wales University Charlotte from 2016-18 and was named USCAA Division II National Coach of the Year in 2018 when they won the National Championship.
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