The Tennessean first reported the decision Wednesday evening and ESPN.com confirmed with sources Thursday.
The decision means Locker, who missed 25 games in three seasons because of injuries, will be playing for his future in Tennessee this season
The price tag to pick up the option was about $14.6 million, according to The Tennessean. Locker, who was the eighth overall pick of the 2011 NFL Draft, is scheduled to make $2.091 million this season.
The deadline for teams to pick up the fifth-year option for players from the 2011 draft is Saturday.
Locker is still expected to be the starter for the Titans in their first season under head coach Ken Whisenhunt.
Locker is recovering from surgery on his foot that ended his 2013 season in November. He has an 8-10 record in his career as a starter. He threw for 1,256 yards with eight touchdowns and four interceptions in seven games last season.