Matt O'Connor is leaving his post as Leinster coach by "mutual agreement" after a disappointing campaign.
The Australian succeeded Joe Schmidt when he left for the Ireland job two years ago and won the 2014 Pro12 title.
But Leinster finished outside the play-off positions this season and forwards coach Leo Cullen will take temporary charge of the team.
"We set high standards for ourselves and for many reasons we did not achieve those highs," said O'Connor, 44.
The former Leicester coach took the Irish province to the Heineken Cup quarter-finals in 2014 and European Champions Cup semi-finals this season.
A 25-20 extra-time defeat by champions Toulon last month was followed by the failure to make the Pro 12 play-offs.
"I am disappointed and frustrated with our form in the Pro12 this season," O'Connor told the club website.
"However, the European journey that we took over two seasons, for a new group of coaches, players and staff, is one that we can be very proud of.
"The dynamic in Europe has changed with meritocracy and fewer teams competing and this has improved the quality.
"We went toe-to-toe with the best and there is no shame in losing to Toulon by the smallest of margins and I'm extremely proud of the group and the character shown."
Leinster said on Thursday that the search for O'Connor's replacement was under way.