Its Grade II-listed building, which dates back to the late 1800s, houses 91 hotel rooms, a glass-domed restaurant-cum-greenhouse, a bar styled like a classic British pub and a grand ballroom set within the original court.
Roman and Williams aimed to enhance the Victorian features of the complex while inserting new decorative accents that reference 1920s New York.
"The challenge of integrating a newly built addition with the inherited architecture of the building materialised a space ripe with dichotomies," said the firm, which was founded by husband-wife duo Robin Standefer and Stephen Alesch in 2002.
"Old and new, hard and soft, New York and London – these principles abound and flourish throughout the building."
Guests enter the hotel's lobby through its original porte-cochere.
The design team added a new main staircase clad in mahogany and framed by a theatrical proscenium arch, while the lobby's chandelier was found in Connecticut, restored and shipped to the UK.
"This space is the nexus of the hotel, both in its acting as the physical compass for guests and wanderers as in its aesthetic junction," said the design team. "It embodies the dichotomy between old and new."
A steel catwalk suspended above the lobby leads guests to their bedrooms while the former police yard beyond the reception, which is covered in a three-tiered glass dome, has been transformed into an all-day dining venue.
The space is filled with greenery from freestanding trees to climbing plants draped down columns to create the impression of being in an Edwardian greenhouse.
Bench seating upholstered in green mohair leads the eye through the centre of the dining space and custom tiles developed by Bantam Tile Works cover the walls.
Tucked just off the Atrium, the hotel's Fireplace Room offers a more intimate dining space while continuing the glasshouse theme with hand-painted botanical wallpaper framed with dark timber panelling.
In the library, which acts as the hotel's living room, vintage velvet seating is surrounded by Sapele millwork shelves. Burnished brass picture lights illuminate oil paintings, paper ephemera and a collection of antique books.
The building's original Magistrates' court has been re-imagined as a formal ballroom with double-height walls covered in a mural by French painter Claire Basler.
Huge chandeliers hang from the original ceiling, which was uncovered by the design team, while hand-blown sconces spring from the surface of the mural to create a dark, moody atmosphere.
Meanwhile in the former police station, Roman and Williams has created the Side Hustle bar as a modern take on the British pub.
Its interior references the golden age of locomotive travel, with walls clad in embossed leather upholstery and millwork panelling while blown glass globes and linen-shaded sconces hang between leather and mahogany booths.
The NoMad Bar in the Atrium on the other hand has an exuberant, maximalist design that celebrates the decorative arts.
It combines Delftware pottery, Italian modernist lighting and furniture in the style of the aesthetic movement – a late nineteenth-century art movement that championed pure beauty and "art for art's sake".
Each of NoMad London's guestrooms features a stone mosaic bathroom, marble vanity and custom Lelievre damask wallpaper.
The 20 suites are designed to resemble well-appointed apartments with their own living and dining spaces as well as claw-foot tubs in the bedroom.
The chain's original location, housed within a Beaux Arts building in New York's NoMad neighbourhood, announced its permanent closure earlier this year as a result of the pandemic.
Photography is by Simon Upton unless otherwise stated.