A native of Los Angeles, California, Cowens was a product of the Kansas City Royals farm system, having been selected by the team in the 1969 MLB draft. He made his major league debut with the Royals in 1974 and played for them through 1979. His most productive season came in 1977, when he batted .312 with 23 home runs and 112 RBI, earned a Gold Glove, and finished second to Rod Carew in balloting for the American League MVP Award.