The specialist contractor will carry out structural demolition, piling and basement box construction, followed by delivery of the 35-storey concrete core for the new tower.
Works are due to start on site this summer.
The landmark scheme is being delivered by Endurance Land, part of the Hong Kong-based Nan Fung Group, and marks a major milestone in the transformation of the prominent City fringe site.
Last year, the developer brought in Multiplex under a pre-construction services agreement to lead the main build. The contractor is now working with the design team to drive efficiencies and embed sustainability principles ahead of full construction.
Designed by KPF, the scheme will provide around 470,000 sq ft of top-grade net zero office space. The 99 City Road tower is targeting BREEAM Outstanding and WELL Core Platinum ratings, with embodied carbon kept below 650kg/CO2/m2.
The new building will improve its connection to the surrounding area through a widened public realm and new square, as part of a major upgrade to the Old Street junction.
Key consultants include: Third London Wall (PM), AKT II (structures), Arup (MEP), Arcadis (cost) and FMDC (facades). Completion is scheduled for the first half of 2029.