The company, whose portfolio includes the main Resort Hotel, the Manor House, the Newbridge on Usk and 10 lodges, is set to complete contracts for the hotel on 31 March.
Celtic Manor Resort chief executive Ian Edwards said: "We are always looking to expand and build upon our successful business at the Celtic Manor Resort whilst continuing to help support the local community and economy.
"Occupancy at the Celtic Manor Resort is currently running at 90 per cent and there are many nights when we could easily exceed our capacity of 400 bedrooms. The additional bedrooms at the newly-acquired hotel will help address our need for more accommodation across all our markets – conference and business, golf and leisure."
Celtic Manor Resort plans to rename the hotel once contracts have been completed and is planning to retain all members of staff.
Hilton Newport includes a bar, lounge and restaurant, nine meeting rooms, a fitness room, swimming pool and spa bath.
“The property is in a wonderful position very close to Celtic Manor and enjoying the same immediate access from the M4 motorway. I am sure it will prove very popular with guests staying at the Celtic Manor Resort," added Edwards.