Sydney's iconic InterContinental Sydney is about to get a whole lot more swish with plans for a $200 million upgrade to all 509 guest rooms and public areas.

But the most stunning part of the package will be a 900m² ballroom extending out from the 10th floor to provide a panoramic vista taking in Circular Quay and the Sydney Harbour Bridge through massive floor-to-ceiling glass walls.

The proposed transformation – which will require approval from the NSW Department of Planning and Environment due to the hotel's unique heritage, which incorporates the former Treasury Building, marks the most significant improvements to InterContinental Sydney for over three decades.

Also on the cards is an expansion of the rooftop Club InterContinental lounge, offering sweeping degree views from the Sydney Harbour Bridge around to Botany Bay.