Talks had been ongoing between Reds general manager Wayne Krivsky and Valentin's agent, Diego Bents.
"It made sense to sign him now," Krivsky said. "We wanted him back and he wanted to be back. He does a lot of things well, the intangibles, too. In the clubhouse, he's well-respected and a quality teammate."
In 156 at-bats over 77 games entering Monday, the switch-hitting Valentin was batting .237 with six home runs and 23 RBIs. Cincinnati's first lefty pinch-hitting option off the bench, the 30-year-old leads the National League with four pinch-hit homers and ranks second with 12 RBIs.
"I'm happy. I want to be here. I like it here," said Valentin, who has been with the Reds since the 2004 season. "They gave me an opportunity. It's a good organization, real professional. We have really good guys here. I'd like to be here more than one more year, a couple of more, and end my career here. But I'll finish the season strong and come back next year and work hard."
Splitting time last season with Jason LaRue, Valentin established career highs by batting .281 with 14 homers and 62 RBIs. But David Ross' addition and emergence to the No. 1 catcher spot has reduced Valentin's opportunities to play.
"I would have liked for him to have gotten more starts than he's gotten," Reds manager Jerry Narron said. "It's just tough when David Ross got to play, and trying to work three guys in is difficult. When one guy is having a really big year, it's real tough."
The 30-year-old Valentin, who is making $1.15 million this season, never complained about his situation.
"Nobody wants to be a bench player, but somebody has to do it," he said. "It's going to be hard. But I'm going to still work, do my job and help the team. Any part, any job, anything, I'll prepare for my opportunity and do my best. Any situation, anytime you need me, I'll be there and I'll be ready."
The Reds traded relief pitcher Mike Burns to the Red Sox on Monday for Triple-A pitcher Tim Bausher.
Burns, who was sent outright to Triple-A Louisville on Friday, posted an 8.78 ERA in 11 appearances for the Reds over multiple callups this season. He was 6-1 with a 1.75 ERA in two starts and 38 relief outings for Louisville. It's possible Boston will use the 28-year-old in its big-league bullpen over the season's final month, which was unlikely to happen in Cincinnati.
Bausher, 27, was 4-3 with a 4.91 ERA in two starts and 35 relief appearances for Pawtucket, and will report to Louisville to help with the Bats' final playoff push.
He will be a six-year Minor League free agent at the end of the season.
Injured closer Eddie Guardado (left forearm tendinitis) has not thrown since Saturday, when he felt some pain during an eight-minute session of catch. Guardado hoped to throw again either Wednesday or when the team returns home on Friday.
"I'm not going to throw until I feel nothing in there," he said. "When I do the exercises, I feel it a little bit. When I don't feel it, I'll pick up a ball. It's gotten better. I always test it."
Right-handed reliever Gary Majewski struck out the side in one inning during his latest rehab assignment outing for Louisville on Sunday.
Reds left fielder Adam Dunn, who is 1-for-19 (.053) against Dodgers starter Brad Penny in his career with 12 strikeouts, was out of Monday's starting lineup as expected. Todd Hollandsworth started in left field and center fielder Ken Griffey Jr. batted cleanup for the first time this season.
With a scheduled off-day on Thursday, Narron said he's considering tweaking his rotation. Eric Milton could be moved up to pitch Sunday at San Diego to stay on his normal four days' rest. That would mean Chris Michalak, Monday's starter vs. the Dodgers, would have his next outing pushed back to next Tuesday against the Giants.
Aaron Harang would get the ball on Labor Day, when the Reds have a rare 5:10 p.m. ET game scheduled after a long trip back from the West Coast. There were no plans to send Harang home a day early to get past potential jet lag.
"We don't have many guys asking for special treatment," Narron said. "When I was with the Rangers, we played a lot of games the next day after coming back from the West Coast. There were a lot of days we'd get in between 5-7 a.m. and play that night. A lot of teams from the West Coast did the same thing. It's not easy."
It was another stellar outing Monday for top Reds pitching prospect Homer Bailey at Double-A Chattanooga. With Krivsky at the game, Bailey allowed two hits without a walk over six scoreless innings. The right-hander struck out eight.
Krivsky, who has been scouting at Chattanooga since Friday, will remain through Wednesday.
Milton (8-7, 5.22) will start for the Reds against the Dodgers' Mark Hendrickson (1-6, 4.79) Tuesday at 10:10 p.m. ET.