The City Quays 3 project is the largest development project undertaken by Belfast to date, providing work space for up to 1800 people.
At 250,000 sq ft, City Quays 3 will be one of the largest Grade A office developments to be built in Northern Ireland.
It will be built near the M3 Lagan Bridge, on a vacant site next to the City Quays 2 building, home to broadcaster UTV among other businesses.
Belfast Harbour chief executive Joe O'Neill said: “We're delighted to award the contract to a local construction company. In addition to supporting 500 local construction jobs, the office will build upon City Quays' success by providing strategic accommodation to meet demand for grade A city-centre office space.”
Farrans regional director Glenn Gilmore said: "Our team has been heavily involved behind the scenes and this announcement is a testament to the professionalism and expertise of all our team working on the project to date."
The City Quays 3 planning application was submitted in May 2017 and sent to Department for Infrastructure for consideration. It was passed three months after new decision-making powers were given to Northern Ireland civil servants in the absence of Stormont ministers.
John Armstrong, managing director of Northern Ireland’s Construction Employers Federation (CEF), welcomed the appointment of Farrans just four months after planning approval was secured. "Farrans, its direct workforce and supply chain will bring a wealth of experience to the project and, at a time of ongoing political and economic uncertainty, the project's commencement will come as a significant economic boost locally," he said.