Both the ERC (European Rugby Cup) and FFR (Fidiration Frangaise de Rugby) ratified the switch of venue on Thursday, boosting the Munster ticket allocation from 3,200 to at least 8,000 for the April 3 clash.
The venue is now the Estadio Anoeta, the 32,000-capacity home of Spanish soccer giants Real Sociedad, after officials ruled out the smaller Parc des Sports Aguilera (12,667).
Biarritz are planning to create a carnival atmosphere for the bumper quarter final weekend. They are inviting Munster fans to view the Leinster v Leicester Tigers and Stade Francais Paris v Newcastle Falcons ties on big screens in their home ground in Biarritz. Shuttle buses are being organised for transportation from Biarritz to and from San Sebastian.
ERC CEO Derek McGrath said: "We are delighted the game will be played at Estadio Anoeta in San Sebastian and commend Biarritz Olympique on the move. Where possible, we encourage teams to play Heineken Cup quarter-finals in larger grounds and the first weekend in April should see over 120,000 fans attend the four games."
Munster Chief Executive Garrett Fitzgerald welcomed the decision. "It cannot have been easy for Biarritz to decide to move from their own ground," he told munsterrugby.ie.
"However, to their credit they took into consideration the needs of Munster supporters and in the end they made what was a good rugby decision. I applaud them for that."
Real Sociedad President Jose Luis Astiazaran added: "We are delighted to have a rugby game of such importance in San Sebastian. All the personnel at Real Sociedad will use our Champions League experience to ensure that we will have a fantastic and memorable occasion."
* Tickets for the game - which will see Spain become the eighth country to host a Heineken Cup tie - will be available from the two clubs, and information on how to get to the ground and buy tickets will be available on the ERC's website, ercrugby.com
Friday, April 1:Toulouse v Northampton Saints - Le Stadium, Toulouse (37,000) - Sport+ / Sky Sports, 7.30pm
Saturday, April 2:Stade Frangais Paris v Newcastle Falcons - Parc des Princes, Paris (40,000) - FR2 / Sky Sports, 3.00pm
Leinster v Leicester Tigers - Lansdowne Road, Dublin (48,000) - RTE / Sky Sports, 5.15pm
Sunday, April 3:Biarritz Olympique v Munster - Estadio Anoeta, San Sebastian (32,000) - Sport+ / Sky Sports / RTE, 3.00pm