Cooper je postal stalni sodnik v Major League Baseball od leta 1999. Delal je v seriji Division Series (2003, 2005, 2006, 2008, 2009, 2011, 2012, 2013, 2014, 2019), v seriji League Championship Series (2004
, 2015, 2016, 2017), Major League Baseball Wild Card Game (2015 in 2016, 2017), 2014 World Series in 2005 All-Star Game. Cooper je sodeloval tudi na World Baseball Classicu leta 2009 in 2013.