Construction has started on new Grade A offices at a development in Belfast's Titanic Quarter, supporting 250 jobs in the building trade.
It is expected Olympic House could accommodate 1,500 workers when complete.
Newry-based construction firm O'Hare and McGovern has been appointed to carry out the build.
It will be surrounded in Titanic by other major entities including Belfast Metropolitan College, Citigroup, the Public Record Office of Northern Ireland, Catalyst, and the tourist attraction, Titanic Belfast.
Olympic House will be made up of two blocks of six and seven storeys including an atrium.
Potential occupants can take out space floor by floor or even on a block by block basis.
Titanic Quarter is part of Belfast Harbour Estate.
Graeme Johnston, Belfast Harbour's property and place director, said: "Belfast Harbour's ambition to develop a thriving economic hub for the region has never been more relevant, as we work with key partners to support the NI economy to 'Build Back Better' from the pandemic crisis.
"Our partnership commitment to develop Olympic House will facilitate 1,500 jobs when complete and we are pleased to play our part in supporting 250 local construction industry jobs, as building work gets under way.
"The development will be one of the most modern office buildings in the city, offering accommodation which will support both growing indigenous businesses and new market entrants."
James Eyre, commercial director for Titanic Quarter, said: "Over £480m has already been invested in Titanic Quarter which has attracted a diversified range of local and global occupiers who have established or expanded their Northern Ireland operations here.
"This is another important milestone as we move from masterplan to reality and we look forward to welcoming interest from occupiers."
Seanie O'Hare, O'Hare and McGovern construction director, said: "This is an exciting and prestigious development in an area of historical importance, and we will be working with some of the best in the construction industry. It sends out a hugely significant message to local, national and international investors that Belfast is continuing to build for the future, and OHMG are delighted to be part of that process."
Earlier this month the Belfast Telegraph revealed two other investments worth nearly £100m at Belfast Harbour are now "under review".
Belfast Harbour intends to spend £45m on quadrupling the size of its film studios at Giant's Park and to invest up to £50m on a new buy-to-let residential development at City Quays 4.
"We're still finalising the consenting process through Belfast City Council for the new extension to Belfast Harbour Studios and in parallel we will keep our investment under review, taking into consideration the timing of recovery after the current crisis," a spokesperson said.
The Harbour also said it hoped to submit a planning application for the buy-to-let development at City Quays 4 over the next 12 months "but, again, we will keep this under review as we emerge from the Covid-19 crisis".