Jim Longley, a top NSW public service CEO, has resigned his post months after Fairfax revealed he was at the centre of a charity payments scandal that is now the subject of an inquiry.

Mr Longley was one of 10 directors who over a decade shared in $2.5 million of "consulting fees" for standing on the board of RSL LifeCare a major charity nursing home provider that receives donations from the public which was founded in volunteer labour.

Jim Longley will step down by the end of the year.

The former state Liberal MP announced he would resign as both CEO of the $2.7-billion Department of Ageing, Disability and Home Care and RSL LifeCare on Tuesday.

"I have decided to take the opportunity to pursue a two year post-graduate degree in the United States with my wife early in the new year," Mr Longley said in a letter to members of the charity