Sadler, a left-handed batsman, progressed through the Academy system at Yorkshire and was named in the England squad for the Under-19 World Cup in 2000 before being forced to return home early due to a knee injury.
He was released by Yorkshire at the end of the 2002 season, joining Leicestershire and averaging 45 in 10 championship innings in 2003.
Sadler helped Leicestershire win the Twenty20 Cup in 2004 and 2006, but managed only 265 championship runs at an average of 16 in 2007.
Derbyshire became his third county when he moved to the County Ground in 2008, a season that brought just 195 runs in six games.
2009 told a similar story - his appearances were limited largely to the limited-overs arena - but he signed a one-year extension for 2010 that would see him captain the second XI.