The auditorium now has 10 wheelchair spaces and there is also an accessible dressing room.
Technical infrastructure throughout the theatre has also been upgraded as part of the redevelopment.
The fly tower has been extended by 4.5 metres (14.8 ft) to accommodate more technically demanding touring productions and the raked stage has been replaced with a level surface.
Hospitality capacity has increased from 200 to 405 people, The former box office has been converted into a café, and a new creative engagement studio has also been created within the building.
Nine-year-old Isla and seven-year-old Ewan from Tollcross Primary School joined lifelong King’s Theatre visitor Charlotte Fabian, 104, as the first members of the public to be welcomed into the redeveloped venue by Capital Theatres chief executive Fiona Gibson.
Their combined age of 120 matches that of the theatre.
