The Brewers called up Singleton and outfielder Blake Perkins from Triple-A Nashville on Saturday and put first baseman Darin Ruf (right knee laceration) and outfielder Tyrone Taylor (elbow sprain) on the 10-day injured list.
"It's been a long journey," said Singleton, who started Saturday's game and batted sixth vs. the Reds. "Right now, I really can't even describe my emotions, my feelings. Definitely grateful."
Perkins, for his part, made a major impact in his recall, hitting a grand slam for his first career homer and driving in five runs.
Perkins hit an RBI single in the second and then capped Milwaukee's five-run third with a drive to right that gave the Brewers a 9-1 lead. He went 1-for-12 and scored a run over his first 10 major league games.
"I was just glad I got the ball in the air," Perkins said. "Then I saw [right fielder Jake Fraley] and I was thinking, 'I hope it goes.' That's out. My mind was completely blank. I don't have words."
Singleton, 31, was such a heralded prospect early in his pro career that he signed a $10 million long-term deal with the Houston Astros in 2014 before ever playing a big league game, but off-field issues hampered his development.
Singleton told reporters he learned about his promotion from Nashville Sounds manager Rick Sweet during the ninth inning of Friday's game.
"When Rick told me, I was just mind blown, to be honest," Singleton said. "It was something that came so unexpectedly at that moment. It was definitely a long time coming."
Singleton batted a combined .171 with a .290 on-base percentage, 14 homers and 50 RBIs with the Astros from 2014 to 2015. The Astros released Singleton in 2018 while he was serving a 100-game suspension under baseball's minor league drug program after a third positive test for a drug of abuse.
Singleton said in 2014 that he was dealing with an addiction to marijuana and had been to a rehabilitation center.
"Once I had time to step away and consider what life really was and what it meant to me, it helped maybe put things in perspective," Singleton said Saturday.
The Brewers signed Singleton to a minor league contract in 2021, after he had batted .321 with 15 homers and a 1.196 OPS in 46 games in the Mexican League earlier that year.
He was hitting .258 with a .384 on-base percentage, .483 slugging percentage, 10 homers and 29 RBIs in 49 games with Nashville this season. That followed a 2021 campaign in which he batted .219 with a .375 on-base percentage, 24 homers, 87 RBIs and 117 walks in 134 games with Nashville.
"It's definitely rewarding," Singleton said about making his return. "There's been a lot of hard work that I've put in. There's been a lot of things I've done emotionally, physically and spiritually to get to this point. Very, very grateful."
The Associated Press contributed to this report.