Mariota, who was the second overall pick in the 2015 draft, will presumably be the backup to Derek Carr, but will provide depth at the quarterback position.
Witten had previously spent 16 seasons in Dallas, but has signed a one-year deal reportedly worth $4.75 million with the Raiders ahead of the 2020 season.
Mariota and Witten strengthen the Raiders offense
Mariota has played in the league for five season and burst onto the scene in his rookie year. However, the writing was on the wall in his fifth season when he was benched for Tannehill, who went on to guide the team to the AFC Championship game.
Although it is likely that the former Heisman Trophy winner will be the backup in Vegas, Mariota will provide excellent cover if Carr was to pick up an injury and miss time on the field.
The Raiders have also added a veteran to their offensive ranks as they’ve agreed a deal for long-term Cowboys tight end Witten.
The 37-year-old retired after the 2017 season, however, after a stint as a commentator for ESPN, he returned last season and finished with 529 yards and four touchdowns from 63 receptions.
Alongside Witten, the Raiders already have an elite player in Darren Waller after the former Baltimore Ravens tight end recorded a breakout season in 2019.