The 40-bedroom hotel, which officially opens on 16 December, will be Eclectic's second city-centre hotel and its fifth overall.
The company also operates Great John Street, Didsbury House Hotel, Eleven Didsbury Park and the 7th Members' Club at MediaCityUK.
O'Loughlin, who owns the company with wife Sally, has spent the last 18 months converting the Grade II listed building in Manchester into a 'baby grand hotel' with five different room types and the King Street Tavern, a 'relaxed' restaurant and bar.
Design has been overseen by Sally, an interior designer, who has given the property 'the same understated luxury' seen at its four others.
"King Street Townhouse, however has its own distinctive and charming character. Every room is unique and furnished with the highest quality fittings and fixtures to ensure that each and every guest has an unforgettable experience," she said.
King Street Townhouse also features a rooftop infinity spa pool with treatment rooms and a gym and a terrace with views of Manchester's Town Hall.
O'Loughlin said: “The regeneration of King Street is significant for Manchester and the opening of our fifth property in this iconic area is an important landmark for us. We have named King Street Townhouse a ‘baby grand hotel’ as it is a small and cosy adaption of the grand hotel.”
The opening of King Street Townhouse is expected to create 70 jobs.