The announcement marks the end of a long disagreement about the terms of Thompson's bequest. The money was left to the Victoria State Opera, which was absorbed by Opera Australia in 1996. It was believed that Thompson, who died in 2002, had not updated her will since 1993.
Opera Australia's claim to the bequest was challenged by Melbourne Opera Company and Melbourne City Opera, who felt that Thompson would have wanted her money to stay in Victoria, rather than be handed over to a national company.
The trust, which is still subject to the approval of the Australian Supreme Court, would be managed jointly by Opera Australia and Victorian Opera Company Limited, a new Melbourne company set up with A$7.6 million in funding from the Australian government.
The new company, which will concentrate on contemporary works and new commissions, was announced in August.
Adrian Collette, chief executive of Opera Australia, said, "I am delighted that a settlement has now been reached and that we have been able to minimize the impact of further court costs, and to preserve so far as possible the value of the bequest for its intended purpose."
Michael Roux, chair of VOCL, said, "The trust will ensure that the proceeds are used wisely and prudently to further develop the art of opera in the state of Victoria."