Contractors are currently being sounded-out for the major restoration scheme designed by Jamie Fobert Architects.
The multidisciplinary design team includes Heritage Architect, Purcell, M&E Engineer, Max Fordham and Structural Engineer, Price & Myers.
The gallery next to Trafalgar Square will close its doors to visitors next June and reopen in spring 2023.
Works from the gallery’s collection will be loaned out to enable them to still be displayed during the closure.
The gallery said: “The project comprises a comprehensive re-display of the Collection, combined with a significant refurbishment of the building, the creation of new public spaces, a more welcoming visitor entrance and public forecourt, and a new state of the art Learning Centre.
“In order to complete the project efficiently and to safeguard visitors, members of staff and the Collection, the Gallery in St Martin’s Place will temporarily close to the public from 29 June 2020 until spring 2023, while essential building works take place.
“During this time, we will continue to share our Collection with the nation as we embark on an ambitious programme of activities which will see hundreds of works travel across the UK through a series of partnerships and collaborations.”