Interplay had originally sold the rights to the Fallout series to Bethesda in 2007, with the condition that it could still produce an MMO based on its universe.
However, there have been continued legal disputes over the rights to the MMO, despite Interplay saying that it will release the project this year.
Bethesda's parent company Zenimax media has now announced a settlement between the two parties, voiding Interplay's rights to the licence and granting it to Bethesda.
Zenimax has also agreed to pay $2 million (£1.29m) as part of the settlement.
> Read our review of Fallout 3
> Read our review of Fallout: New Vegas
A second lawsuit which saw Bethesda take action against the developer of the MMO, Masthead Studios, has also been settled.
As part of the initial agreement, Interplay could not sub-licence the rights to other studios to develop the project. Masthead Studios has now acknowledged it had no legal right to Fallout and will not pursue Bethesda's intellectual property going forward.
It was added that Interplay will continue to own the rights to Fallout, Fallout Tactics and Fallout 2 until December 2013, when they will become the sole property of Bethesda.
Watch a trailer for Fallout: New Vegas below: