Greater London House will see its entrance, steps, and rooftop reimagined as part of a new refurbishment plan by Lazari Investments.
It comes after Camden Council’s decision to grant planning consent last month.
Melvyn Hale, group director of developments at Lazari, said: “Our continuing investment maintains the building’s relevance in London’s office market and its status as a key employment location in the borough.
“A factory is a great starting point for an office building.
“Its structure naturally gives you large, open spaces with plenty of light.
“Not many offices give you four metre ceiling heights.
“The latest, substantial upgrade will bring a variety of outdoor spaces that can accommodate individual relaxation, socialising or meetings, large and small.”
The proposals include a new sixth-floor rooftop terrace, a larger entrance, an expanded reception area, and upgraded communal workspaces.
The works will add 85,000 square feet of office space, with floor-to-ceiling heights of 3.7 metres, new air conditioning, and private terraces.
Located in Mornington Crescent, Greater London House houses tenants including ASOS, Revlon, the British Heart Foundation and Clarion Housing.
The building, originally the Carreras Black Cat cigarette factory, was built in 1928 and later converted into 376,000 square feet of office space.
Lazari Investments first acquired the property in 2007 and completed a major refurbishment in 2019.
The latest plans include a 6,157 square foot reception, a communal roof terrace, and new landscaped terraces along Hampstead Road.
These terraces will feature seating areas and improved connections to the park opposite.
The scheme also incorporates sustainability measures, including the relocation of existing solar panels and the addition of 16 new panels.
The roof terrace will include planters, green walls, and a green roof to support biodiversity.