Forrest was drafted by the Washington Football Team in the fifth round (163rd overall) of the 2021 NFL draft.[6] He signed his four-year rookie contract on May 13, 2021.[7] He was placed on injured reserve on September 1, 2021.[8] He was activated on November 2, 2021.[9]
In Week 1 of the 2022 season against the Jacksonville Jaguars, Forrest had his first career start and recorded five tackles, two deflected passes, a forced fumble, and a game-sealing interception, which was the first of his career, late in the fourth quarter.[10] In Week 10, Forrest recorded an interception and a fumble recovery in Washington's 32-21 upset victory over the undefeated Philadelphia Eagles.[11][12] Before the Week 11 game, Forrest was made the starting free safety taking over for Bobby McCain.[13] Forrest recorded his third career interception in Washington's 23–10 victory over the Houston Texans.[14] He finished the 2022 season with 88 tackles, four interceptions, nine pass breakups, two forced fumbles, and one fumble recovery over 17 games (starting 11 of them).[15]
On October 10, 2023, Forrest was placed on injured reserve for a shoulder injury.[16]