Porter (26) and fellow prop Tadhg Furlong have become mainstays of the starting XV under head coach Andy Farrell.
The 42-time-capped Porter suffered the injury during Ireland’s 57-6 thumping of Italy this past Sunday.
“Following a scan on his injured ankle, Andrew Porter has been ruled out of the remainder of our #GuinnessSixNations campaign,” the Irish Rugby Football Union (Irfu) tweeted.
“He has returned to @LeinsterRugby and his medical treatment will be managed by the Leinster Medical Team.”
Porter will miss Ireland’s tricky away match against England on 12 March and the final game at home to Scotland a week later.
Both Ireland and England have lost a game apiece but still entertain hopes of the title – they must hope Grand Slam-chasing France slip up against either the Welsh on 11 March or England in Paris on 19 March.
© Agence France-Presse