To make room for Timlin on the roster, the Red Sox will designate right-hander Bryan Corey for assignment on Friday.
Corey was informed of the move after Thursday's 12-6 win over the Tigers.
"The move will be done tomorrow," said Red Sox manager Terry Francona. "Again, it's not official, but I think out of respect to him, we thought we should talk to him tonight."
Corey struggled mightily in the early stages of this season, posting a 14.54 ERA over six games. The Red Sox now have 10 days to either trade him, release him or assign him to the Minor Leagues, should he clear waivers.
The Red Sox are happy to have the long-trusted Timlin back at their disposal.
Though Timlin displayed better arm strength this Spring Training than in recent years, a freak injury forced him to start the season on the disabled list.
Pitching against the Blue Jays in an exhibition game on March 19, Timlin suffered a laceration of his right ring finger while trying to get out of the way of a grounder.
The injury required several stitches.
Timlin pitched twice at Triple-A Pawtucket before being deemed ready to pitch for the Red Sox.
"[I] threw strikes, got people out," said Timlin.
It was the second year in a row he opened the season on the disabled list.
"Maybe I need to make an annual trip to Pawtucket every year, I don't know," quipped Timlin.
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.