Neptune Investments has let the 21,500 sq ft Observatory office building in Liverpool's Queen Square to Liverpool Mutual Homes on a 25-year lease.
The housing association will relocate 180 staff from nearby Commutation Row at the end of Lime Street and City Point in Great Homer Street. The Observatory has been vacant since Liverpool Vision left to move to Downing's Capital in April 2008.
Danny Hynd, director of Neptune Investments, said: "We have an active asset management strategy which has ensured that Queen Square remains as popular as ever. It's a major part of the city's infrastructure and we're delighted to welcome LMH to the square."
The Observatory was designed by Liverpool-based architects Falconer Chester Hall and completed in 1998.
Mason Owen and Hitchcock Wright & Partners are the letting agents.