Harvey, 30, was designated for assignment last month by the Los Angeles Angels, with whom he signed a one-year, $11 million deal before the season.
Harvey was 3-5 with a 7.09 ERA in 12 starts for the Angels in 2019.
Once dubbed "The Dark Knight," Harvey was among baseball's most dominant starters for a time with the New York Mets. He started the 2013 All-Star Game at Citi Field but hurt his elbow later that summer and never consistently regained his 98 mph fastball or command following Tommy John surgery.
Information from The Associated Press was used in this report.
Chapman belts two homers in A's win
Matt Chapman hits two solo home runs in the Athletics' 9-5 win vs. the Giants.