The addition of Anderson concluded a combination of roster moves on Tuesday and Wednesday.
Starting pitcher Kyle Davies, who was scheduled to start Wednesday, is also back on the roster, while the contracts of outfielder Ryan Freel and pitcher Sidney Ponson were both designated for assignment.
Anderson hasn't played since July 22, but part of that long gap can be attributed to the newest addition to Anderson's family.
Anderson and his wife welcomed their first son, Easton Aaron, on Tuesday morning near their home in Somerset, Kentucky.
Anderson said he was getting a little antsy waiting for the baby while his new team waited for his services, but he said Royals general manager Dayton Moore and manager Trey Hillman had been supportive throughout the past week.
The baby finally arrived at 8:11 a.m. CT on Tuesday morning. Anderson stayed the night in the hospital on Tuesday, and then woke up at 4 a.m. on Wednesday to catch a plane to Kansas City.
"It was one of those things, it was out of our control," Anderson said. "But it worked out. I was able to see the baby when he was born."
Now it's back to baseball. The Royals need speed and defense in their outfield, and Anderson thinks he can provide that.
"The biggest tool I can bring to this team I'd probably say is my legs," said Anderson, who had 13 steals in 15 chances this season for Detroit.
"Guys that can run like that, they make a lot of things happen," said Royals bench coach John Gibbons, who filled in for Royals manager Trey Hillman on Sunday and Monday and answered questions again on Wednesday. Hillman, who was dealing with a personal matter at home in Texas, was scheduled to return for the start of Wednesday's game.
For now, the coaching staff and front office will have an opportunity to evaluate Anderson for the rest of the season.
"I guess they ran out of room over there in Detroit," Gibbons said. "We feel lucky to grab him."
Anderson made his Major League debut in 2007 with the Astros, playing in 20 games. He was traded to Atlanta before the '08 season and played in 40 games for the Braves in '08.
There were limited opportunities for playing time in Detroit, but Anderson is hopeful that will change in Kansas City.
"I look forward to doing whatever it is they ask me to do," Anderson said. "I've never been a guy that's demanded anything. I'm not really in that position.
"I'm gonna play hard every day. I don't take this for granted ... so I just look forward to playing hard and doing the best I can."