Harlequins director of rugby Conor O’Shea will leave The Stoop when his contract expires at the end of the season after six years in charge.
O’Shea, 45, who led Quins to the Premiership title in 2012, is expected to become Italy’s new head coach.
The club, which also won the Amlin Challenge Cup and the LV Cup during his time there, says it is searching for the Irishman’s replacement.
“The end of this season is the right time for me to move on,” said O’Shea.
“We have a very talented group of players and coaches who are intent on securing silverware this season, and that is my sole focus and where all our efforts are concentrated.”
O’Shea won 35 Ireland caps between 1993 and 2000 and spent 10 years at London Irish as a player and coach before taking over at Quins.
He took the job in the aftermath of the ‘Bloodgate’ scandal that saw Dean Richards resign.
“All of us at the club are of course disappointed that Conor will be leaving us at the end of this season,” said Harlequins chief executive David Ellis.
“Conor took over after a difficult period in our history. Under his leadership and through his determination, energy and positive approach he has helped restore pride in our famous shirt and rejuvenate the playing style for which we are known.
“On behalf of all of us associated with Harlequins, I would like to thank Conor for his tireless and selfless commitment over the last six years, guiding us through our most successful period on the field.
“Conor will leave the club in a significantly better place than he found us and for that we are all grateful to him.”
Quins are currently third in the Premiership table, six points behind leaders Saracens.