McLaren was originally lined-up for the job and organised a suppliers open day for the project in April.
But industry sources said McLaren was unable to agree final terms with the client and Ardmore is now the main contractor.
The project has been designed by architect Robert Partington & Partners and will see the existing brick façade retained while the remainder of the building is demolished to create a new basement and six-storey residential block and new mews houses.
Keltbray has already completed the majority of demolition work.
The scheme is due for completion in mid-2019 and will provide 40 new high-specification private apartments and three affordable units within the mews.
Ardmore Director James Byrne said: “We are very proud to have been awarded this contract on the back of a lot of hard work with Londonewcastle and the design team to ensure the project could go ahead.
“Ardmore has a well-established working relationship with Londonewcastle that has allowed us to use our experience of the London residential sector to bring this exciting project in line with our client’s budget without a single compromise on quality.”
Baerbel Schuett, Development Director at Londonewcastle said: “We are delighted to be working with Ardmore again and excited to see Parker House get underway.
“We are looking forward to building on our existing accomplishments with Ardmore in order to deliver high quality housing across London”
The existing Parker House façade sits behind it’s steel retention scheme