The Labour Party's general secretary David Leach is resigning to take up a position as director of communications with the charity Goal.
He was announced as former general secretary Ita McAuliffe’s successor in November 2014.
Tánaiste and Labour Leader Joan Burton thanked Mr Leach for his work.
“David has been a loyal, hardworking and valued servant to the party, through good times and bad, and has made an immense contribution to Labour. I wish him well in his new position,” she said.
The process of appointing a replacement will get under way “in due course”, according to a Labour spokesman.
Mr Leach had previously served as policy director under former party leader Eamon Gilmore. He retained his party organiser duties while serving as general secretary.
His resignation is effective from June 14th.