Harvey, 31, was a former ace with the New York Mets. He signed a one-year, $11 million deal with the Los Angeles Angels last season but was released in July after going 3-5 with a 7.09 ERA in 12 starts.
Once dubbed "The Dark Knight," Harvey was among baseball's most dominant starters for a time with the Mets. He started the 2013 All-Star Game at Citi Field, but he hurt his elbow later that summer and never consistently regained his 98 mph fastball or command after Tommy John surgery.
Harvey has some history with the Royals. The right-hander was the Mets' Game 5 starter in the 2015 World Series against Kansas City. He pitched eight shutout innings and then talked manager Terry Collins into leaving him in in the ninth, when he gave up two runs to send the game into extra innings. The Royals won the game in the 12th and clinched the World Series.