Mattingly was named National League Manager of the Year on Tuesday after guiding the Marlins to their first postseason appearance since 2003. Miami reached the playoffs despite dealing with a COVID-19 outbreak in its clubhouse.
Mattingly, who guided Miami to a 31-29 record this past season, became the first Manager of the Year for the Marlins since Joe Girardi in 2006.
Meanwhile, Cash won the Manager of the Year award in the American League for guiding the Rays to a division title, the AL's best regular-season record and a berth in the World Series.
The Rays posted a 40-20 record in the regular season and clinched the AL pennant before falling in six games to the Los Angeles Dodgers in the Fall Classic.
Cash, who finished third in the balloting for AL Manager of the Year in each of the past two seasons, became the second manager in Rays history to win the award. He joined Joe Maddon, who captured the award in 2008 and 2011.