Unite plans to build the £30m hall at the Chaucer House site on Isambard Brunel Road by 2018.
The acquisition further strengthens Unite’s long standing relationship with the University of Portsmouth, currently ranked 59th according to The Times Higher Education Rankings.
In 2016, all 2,200 of Unite’s beds in the city will be operated under nominations agreements demonstrating the strength of the partnership that extends back over 15 years.
Richard Simpson, managing director of property for Unite Students, said: “The acquisition demonstrates our ability to continue to secure high quality sites in line with our target returns.
“Unite has a strong understanding of the market in Portsmouth and a very positive working relationship with the City Council which has been built over a number of years.”
Leader of Portsmouth City Council Cllr Donna Jones said: “Providing high quality managed student accommodation in the city is key to assisting Portsmouth’s housing shortage. The more student accommodation we have in the city, the more private family homes will come into the rental market easing overcrowding in the city.
“Unite are a long term established student accommodation provider and I welcome the development in the city.”