Newcastle's Roundhouse building has been added to the State Heritage Register.
Heritage NSW executive director Sam Kidman said the former Newcastle council administration centre represented an important example of late 20th century international modernist style of brutalist design.
The building was constructed between 1972 and 1977 and opened 23 June 1977.
It was designed by Australian architects Romberg and Boyd in association with Wilson and Suters.
Local architect Brian Suters, who was part of the original architectural design team, nominated the iconic structure for state heritage listing.
Newcastle council sold the building, variously known as the Champagne Cork, Wedding Cake, Egg Cup and Shuttlecock, to Syrian billionaire Ghassan Aboud in 2018.
Aboud's Crystalbrook Collection hotel business converted it into a five-star hotel - a process that involved the addition of a ninth floor to the original structure.
"I am impressed at how the original construction and design has been conserved and celebrated, and how well the adapted building fits in with all its state heritage neighbours in this wonderful civic precinct," Mr Howarth said.
"The renovation of the former city administration centre into the Crystalbrook Kingsley hotel has revealed a highly successful adaptation of an historically important building.
Crystalbrook Kingsley's general manager Carl Taranto said the hotel was designed to celebrate the city's past and future.
"One of the group's commitments to the hotel development was to celebrate what the building was, as well as what it is to become," Mr Taranto said.
Reports from the time of the building's construction said the site's excavation was complicated by an unusually high water table.
The solution was the construction of an underground dam around the building's perimeter.
