The bar, gallery and auditorium have also been refurbished.
Over the course of the weekend, there were broadcasts of the musical productions, 42nd Street and Cats, public tours of the building and a celebratory evening with some traditional music from Alistair Anderson and band.
Northumberland County Council has contributed £2.5million towards the cost of the work, with the Playhouse raising a further £800,000.
Take a look at these 19 pictures from the grand opening
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