Surveyors Lambert Smith Hampton will move from 79 Mosley Street in St Peter's Square to 3 Hardman Street in Manchester's Spinningfields by the end of the year.
LSH will sublet 10,000 sq ft from BDO for the 13 years remaining on the lease, effectively taking one wing of the sixth floor.
LSH, which has been on Mosley Street for 75 years, originally wanted to take space in Orchard Street's Belvedere on Booth Street but was outbid by rival CB Richard Ellis.
Roger Tunnicliffe, head of LSH's Manchester office, said: "We plan to expand the Manchester office [which employs 75 people] quite considerably in the future.
"We are currently in an old building on three floors and it is just not suitable for today's business. We are very excited about being in the city's vibrant new business district."
BDO was advised by Drivers Jonas Deloitte.