Something unlikely to be altered; a fait accompli: If Ben shook your hand, it was a done deal/ President Bush's enormous popularity may appear to make his re-election a done deal(1980s+)
Idioms and Phrases with done deal
done deal
An irrevocable agreement, as in Once you've signed the lease, it's a done deal. This slangy expression, first recorded in 1979, may have come from done thing, originating in the late 1600s.