The Knightsbridge-based firm specialises in offsite rooftop extensions and has built luxury homes on top of existing buildings in areas such as Chelsea, Knightsbridge and St. John's Wood.
It is currently working to secure and deliver a further nine projects across the capital, with a gross development value of over £120m.
High Street Group Chairman, Gary Forrest, said: "A couple of years ago, the government welcomed a proposal to help address the housing shortage in London through the development of modular homes on top of existing buildings.
"We believe there is a huge potential in this innovative idea and have researched potential sites, as well as the associated considerations of planning, design, sustainability and construction.
"What we lacked was the expertise to deliver projects and that is why we have acquired First Penthouse.
"The deal adds people with practical and successful experience of rooftop development to our team, which will, I am sure, significantly accelerate our involvement in this market place."
Patrick Brightman, managing director with First Penthouse, added: "With the benefit of the group's support and investment, we can exploit many more opportunities across London and further afield and can accelerate the number of developments we undertake, as well as our aspiration to build our own offsite modular construction company."
A study by Interdisciplinary Design Consultancy HTA LLP identified that in the Borough of Camden alone, there are 475 potential rooftop sites, which could deliver 2,485 homes.
Across Greater London, it identified over 14m sq ft of developable roof space, which could deliver almost 180,000 properties.
