The capacity of Leinster’s RDS Arena is to be extended to 25,000.
The stadium in Dublin 4, with a current capacity of 18,500, is home to the current Pro12 rugby champions and the Dublin Horse Show.
The announcement came at the launch of an international architectural design competition, the first step in the redevelopment of the arena.
Work is not expected to start until April 2016 at the earliest.
Leinster will continue to play their home games at the RDS during the redevelopment.
Speaking at the announcement, Leinster coach Matt O’Connor said: "The key challenge is retaining the special atmosphere and experience that the RDS is for the players and the supporters.
"They feed off each other and it is vital that this element is retained.”