Middlebrooks has hit in eight straight games at Pawtucket, batting .333 (11-for-33) with two home runs and a double.
He was demoted to Pawtucket on June 25 after batting just .192 in his first 53 games. The Red Sox put Brandon Snyder on the disabled list as a corresponding roster move.
Middlebrooks' promotion does not preclude the possibility of highly touted prospect Xander Bogaerts also being called up in the coming weeks. Bogaerts could be used the way Jose Iglesias was, in a rotating system with shortstop Stephen Drew and occasionally filling in at third.
Drew has been one of Boston's hottest hitters of late, batting .432 (16-for-37) in a 10-game hitting streak with two home runs and eight walks.
Middlebrooks, who was enjoying a terrific rookie season (.288, 15 home runs, 54 RBIs in 75 games) until his right wrist was fractured when struck by a pitch from Cleveland's Esmil Rogers on Aug. 10, 2012, came to camp this spring as the starting third baseman, a job he had wrested from Kevin Youkilis last year.
He got off to a fast start this season, hitting three home runs at Toronto on April 7, the team's sixth game of the season. But he then plunged into the worst slump of his professional career over the next 14 games, batting just .093 (5-for-54), striking out 20 times and walking just once.
He also injured his ribs in a collision with catcher David Ross on May 7. Then, on May 24, Middlebrooks went on the disabled list with a lower-back strain, missing 16 games.
At the time of his demotion, Farrell said he explained to Middlebrooks that he should not expect an immediate recall. Of greatest concern to the club was Middlebrooks' alarming strikeout-to-walk ratio: 60 K's, nine walks.
"Will will be getting regular at-bats," Farrell said at the time. "For him to get back on track, he needs every-day at-bats.
"His skills haven't gone backward. He's still a very talented player. He needs consistent work that will allow him to replicate his swing. This isn't uncommon for a young player, to take a step back now for the bigger picture.
"He will be our everyday third baseman ... (but) this isn't going to be a numbers deal. It's not a matter of hitting .310 and coming back here."
Middlebrooks is returning after 45 games for the PawSox, in which he batted .268 with 10 home runs and 35 RBIs in 179 at-bats. He showed an improved selectivity at the plate, drawing 16 walks to 38 strikeouts.
Middlebrooks acknowledged his frustration at being passed over while the Red Sox promoted others ahead of him.
"Since I've been here I've seen a lot of my teammates get called up to Boston," he wrote in a diary for ESPNBoston.com. "How have I dealt with not getting the call? Well, of course I want it to be me. Who doesn't want to get called up to the big leagues? It's what you work for your whole life and play for, but I've had to put that frustration aside. I've realized when I'm frustrated or worried about that, I'm not focused on the right things to get me back to the big leagues. The first couple of times it happened, yes, I was frustrated. I wanted it to be me, of course. The last couple of times, I tried to look at the big picture. I know if I'm not focused on the right things, I'm not going to get back there.
Middlebrooks also indicated that his back issue had not been fully resolved.
"I just want to be the player that everyone has seen," he wrote. "When I can get my body back to normal, I feel like everything will fall into place. It's not an excuse because there have been plenty of other factors, like my approach at the plate, that snowballed on me. I just want to get back and help us win a World Series."