The 22-year old Welsh full-back has signed a three-year deal with the Royals, following Adrian Mariappa from Watford, and is looking forward to getting started with the Premier League club after positive talks with manager Brian McDermott, director of football Nick Hammond and chairman Sir john Madejski.
"Having spoken to the manager, Nick Hammond and the Chairman today, everyone has made me feel really welcome and I'm really looking forward to this opportunity," he told the club's official website.
"If you form a team spirit, a togetherness, you'll always do well in football - and if you work hard you'll get your rewards. Reading have certainly done that in the last few years. Hopefully that can carry on. Right now, I need to focus on impressing everyone at this club and I'm really excited to get going."
Gunter has been with Forest since he joined from Tottenham in 2009 after his first senior spell with Cardiff City between 2006 and 2008 after coming through the Welsh clubs youth academy.