Ramirez, who was not in the starting lineup Monday night against Colorado, had been out all season since tearing a ligament in his right thumb during the championship game of the World Baseball Classic. He had surgery on March 22.
Ramirez could start Tuesday's game, which happens to be Hanley Ramirez bobblehead night at Dodger Stadium.
The three-time All-Star played two rehab games for Class-A Rancho Cucamonga last weekend, going 3 for 6 while spending 12 innings at shortstop. He worked out with the big club at Dodger Stadium on Monday afternoon, and Los Angeles decided to activate him.
"I'm ready to go," Ramirez said. "It's not 100 percent, but I can defend myself on the field. I just want to be in there. I don't want to wait any longer. I think I can play."
Ramirez will play with a splint on the thumb.
"I've just got to get used to it," he said. "If I want to play, I have to play with it, and that's fine."
Kershaw, who threw eight dominant innings in a 2-0 win over the Brewers on Sunday, left the team to tend to what manager Don Mattingly called a "personal issue."
The 2011 NL Cy Young Award winner was placed on the bereavement list, which requires a player miss a minimum of three games and a maximum of seven. Mattingly said he expects to have Kershaw back in time to take his next turn in the rotation Friday against the San Francisco Giants.