The 48-bedroom facility will specialise in cardiology, cardiac surgery, oncology and orthopaedics and will feature four operating theatres and 28 consultation rooms.
The new hospital, due to open in spring 2021, will provide both outpatient and inpatient services as well as physiotherapy and diagnostics.
Nuffield Health received approval from the City of London to renovate the dilapidated former pathology and residential staff quarters buildings in 2018.
The charitable hospital group partnered with Barts Health NHS Trust, which runs St Bartholomew’s Hospital, to lease the buildings.
The site will be physically and operationally independent from Barts Health NHS Trust and staffed by Nuffield Health.
Maxine Estop Green, hospital director at Nuffield Health, said: ‘It is always something to celebrate when you reach this stage of a major build, particularly with a project as complex as this one.
‘The history of the site and the constrained space in which the team have had to work have presented significant challenges but it has been a delight to mark the completion of the main build which means we are on schedule to open the City’s first independent hospital next spring.’
In 2014, Barts Health launched a competitive tender for a 30-year contract to build, finance and operate a private patient facility on one or more of its sites with a focus on cardiovascular treatments. Nuffield was chosen as the preferred bidder in 2016.