The developer is planning a major refurbishment and extension of the 47,500 sq ft office building once the current tenant’s lease is up next year.
The seven storey building was originally developed in 1992 behind a 19th century façade.
It becomes the fourth building in Helical’s Manchester portfolio.
The block also includes two small retail units totalling 4,000 sq ft which are also let until 2018 and will then benefit from some smaller refurbishment work.
Will Parry, Asset Management Executive at Helical, said: “This off-market transaction further complements our existing portfolio in Manchester, where occupier demand for well-located, good-quality assets in the centre remains strong.
“The supply of Grade-A space is currently near an all-time low and there is a limited development pipeline, so Trinity Square represents an exciting proposition for us.
“Capitalising on these positive market dynamics, the asset is in an area that is undergoing significant transformation and offers attractive reversionary potential following the capital expenditure programme, as rents in the area start to reflect the quality of local occupiers.”