The agreement overturns an earlier decision by the club to remove Cooper from the Wales squad before the final Invesco Perpetual Series international.
A deal to free Cooper for Wales duty was brokered by welsh Rugby Union Group Chief Executive Roger Lewis, and ensures the scrum half can now contest to retain the number nine shirt he has worn for the games against South Africa and New Zealand.
There has been an issue over the availability of England based Welsh squad players since the PRL, which represents the English Premier Division clubs, advised them to return to club action after the Wales versus New Zealand game.
The international against Australia falls outside the IRB window of November internationals and the WRU has no contractual agreement with English clubs to cover player availability.
Throughout the week detailed talks have been taking place involving Roger Lewis of the WRU, Martyn Thomas, the chairman of the RFU management board and the Gloucester Chairman Tom Walkinshaw.
Roger Lewis said: “I am delighted to have been able to secure the release of Gareth Cooper for this important international match against Australia.
“I want to publicly thank Martyn Thomas and Tom Walkinshaw for helping to conclude this arrangement in the face of difficult circumstances and against a tight deadline.
“The whole issue of player release for international duty is complicated and can be pressured so I fully appreciate the difficult decisions involved in reaching a workable conclusion.
“I have been able to broker a rugby solution to this matter because Martyn and Tom have been open to frank and honest debate which focused on the best interests of the game and the player involved.
“Gareth is a proud Welshman and the important thing is that he can now focus his mind on preparing for next weekend with confidence.
“The Welsh Rugby Union recently reverted to legal action when there was no achievable resolution in a player release issue which was a clear breach of existing contracts. In this case we have been able to talk through the problem and that took determination from all sides.
”We all understand the dynamic involved when a club needs a contracted player but his country also requires him but this issue with Gloucester has proved we can resolve our difficulties if the parties are prepared to talk through all the concerns.”
Martyn Thomas said: “There are genuine concerns from all perspectives on this issue and I am delighted we have been able to agree a solution which benefits rugby.
“The welfare of the player is vitally important and it is right and proper that Gareth Cooper can endeavour to retain the Wales number nine shirt he has earned through this series so far.
“He is also a proud and committed Gloucester player so I am sure it will be a relief to him that all parties have been involved in reaching this agreement.”
Tom Walkinshaw added: “We have defended the right of Gloucester to play the best possible team available from our squad within the terms of any agreements which are in place.
“It is important in rugby that we also take a view on what the team requirements are allied to the best interests of all the players we have available. On this occasion I am pleased that we have been able to reach a sensible understanding.”
