Garrett missed each of Cleveland's past two games after being placed on the list, but the Browns won both contests.
With Garrett back in the fold, Cleveland will look to improve to 9-3 when it visits the 8-3 Tennessee Titans on Sunday.
Garrett was a leading Defensive Player of the Year candidate before landing on the reserve/COVID-19 list Nov. 20, and despite missing two games, he is still likely in the mix.
The 2017 No. 1 overall pick is tied for second in the NFL with 9.5 sacks, trailing only Los Angeles Rams defensive tackle Aaron Donald, who has 10. Garrett is also tied for the lead in forced fumbles with four.
Garrett entered the season having recorded double-digit sacks in back-to-back seasons, including a career-high 13.5 in 2018.
While Garrett's return will provide a huge boost to the defense, Harrison's absence could hurt the secondary significantly.
The third-round pick out of Alabama in 2018 was acquired by Cleveland from the Jacksonville Jaguars prior to the season for a 2021 fifth-round draft pick.
Harrison has started six of the 10 games he's appeared in, racking up 32 tackles, six passes defended, one sack and one interception, which he returned for a touchdown.
Harrison is required to miss at least three games, meaning he will first be eligible to return for the Browns' Week 16 game at the New York Jets.
Andrew Sendejo and Karl Joseph figure to serve as the starting safeties with Sheldrick Redwine and Tedric Thompson providing depth.
The Browns have already clinched their first season with a record of .500 or better since they went 10-6 in 2007, and a win over Tennessee would go a long way toward positioning them for their first playoff appearance since 2002.