Allen had been making progress throughout the week and HC Sean McDermott left the possibility open of him being cleared today.
Buffalo would have had to start Matt Barkley in place of Allen had he not officially cleared the protocol today.
Allen, 23, is a former first-round pick of the Bills back in 2018. He signed a four-year, $21,265,508 contract with the Bills that includes a $13,545,824 signing bonus.
The contract includes a fifth-year option for the Bills to pick up in 2021.
In 2019, Allen has appeared in four games and completed 60.3 percent of his passes for 903 yards, three touchdowns and six interceptions. He had also rushed for 131 yards and three touchdowns.