Deloitte is relocating its Belfast operations to a new development in the city centre.
The consultancy firm has rapidly grown its presence in the city in recent years and expects to have 1,000 staff by 2022.
It will become the anchor tenant of Bedford Square.
Jackie Henry, senior partner at Deloitte in Belfast, said the move reflects the firm's confidence in the city.
"Deloitte's operations have been growing rapidly over the past few years, driven by increased requirements for our services across traditional areas and our wider expertise in exciting new areas such as digital analytics and robotics," she added.
"This new office will bring Deloitte's expertise in Belfast together under one roof."
Bedford Square is a new office scheme in the city centre.
It is being developed by Cookstown firm McAleer and Rushe and will involve refurbishing and extending the Ewart's warehouse on Bedford Street.
Stephen Surphlis, Property Director in McAleer & Rushe said: "Securing Deloitte's commitment is a significant milestone in the delivery of this strategic development."
When the development is complete it will be Deloitte's largest UK office outside London.