The backup quarterback featured for the NFC North champions for the first time last season, having joined the Packers in 2010.
The 28-year-old told the team's official website: "For a lot of guys it's their first shot out there. But coming off a game like that, I'm extremely confident and I look forward to the pre-season.
"You get to bounce questions off three different guys and get three different sides of the game. So it's a great system right now and a great place to be. It's a fun time for backups and it's your chance to really get to play.
"It's a chance to grow and learn, and as a group you kind of grow together. I think the later we went in the pre-season, the sharper we got. Hopefully, we can start a little further along than we did last season."
Harrell played in four games for the Packers as backup to Aaron Rodgers in 2012.