Northridge became chairman in January 2009.
Upon stepping down from the position on June 30, he will be replaced by Gary McGann, who currently serves as a non-executive director after joining the bookmaker in November last year.
“It has been a pleasure to have had the opportunity to serve on the Board over the past 11 years,” Northridge said.
“The group has made great strides in that time due in no small part to the endeavour and commitment of my Board colleagues and of management, present and past, for which I thank them.”
Confirmation of Northridge’s departure came as Paddy Power also unveiled a trading update for the period from January 1 through to May 11.
The bookmaker said that despite having been hit by unfavourable sports results in the period, it was able to post year-on-year growth across the entire business.
Total net revenue was up 26% in comparison with the same period of last year.
Total group sports betting stakes were up 21% year-on-year, with online sports wagering experiencing 24% and retail a 14% hike.
Paddy Power’s Australian business experienced heavy growth in the period, with net revenue up 43% on last year, while revenue from its overall online operation was up 31%.