"Glenn is a true pro who has quickly become a valued contributor to our organization both on and off the field," general manager Trent Baalke said. "He is a quick study and a very good football player that has earned this extension, and we look forward to his future contributions."
A coaching staff favorite, Dorsey was named the 49ers Defensive Blue Collar Player of the Year for his efforts in 2013.
Dorsey's status is in doubt for the bulk of the 2014 season after recent surgery to repair a torn biceps in his left arm.
Clearly confident that Dorsey will recover from his injury, the 49ers are planning for the future at a bargain rate.