An expected 1000 jobs are to be based in the building.

Its construction parallels the signing of a 12-year lease for five floors of the Lang's Corner building at the junction of Crown and Kembla Streets, by superannuation group Mercer Administration Services, owned by international company Marsh & McLennan.

Read more: Lang's Corner dig uncovers old Wollongong wine store and newspaper office

Anchor tenant Mercer will remain based at its facility at Coniston until 2022, before moving to its new Illawarra office and commencing its 12-year lease.

The Head of Mercer's Operations business in Wollongong, Craig Rice said its relocation will "create a leading-edge workplace for employees and position ourselves for long-term success".

"Following the acquisition of Pillar in 2016, it was very important to us that we find the perfect location that would grow with the Mercer Wollongong team over the years to come," he said.

"Our Lang's Corner office will allow us to create an environment that meets the changing needs of our workforce, with greater links to the community."

Mr Rice said they would have their entire operation, comprised of more than 500 staff, moved across to the new building.

"We wanted to be in the centre of Wollongong, and wanted to be modern and innovative," he said.

The site until recently housed the 1930s Lang's Corner building.

Lang's Corner was razed last year to make way for the multi-million dollar office building, which will - at council orders - incorporate the demolished facade of the former building into its design.

Construction is due to be completed in late 2022.

Knight Frank Illawarra completed the Mercer Lang's Corner lease and is managing opportunities for potential tenants.

Managing partner Ben Mostyn said the Mercer agreement not only consolidated significant existing jobs in the Illawarra, but is delivering a site that expands employment opportunity in Wollongong's centre.

He said there had been interest from other parties in being located there.

"This is the largest ever non-government lease in the Illawarra," he said.

"It shows faith in our city's and region's future and should encourage other businesses demanding A-class offices that Wollongong and all its support services can deliver for them."

Pupovac Constructions is building the office-commercial complex.

Its previous projects in Wollongong's commercial centre include the Australian Taxation Office centre and renewal of the ANZ Bank building.

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