The property firm is buying Atlas's 5,575-room portfolio, according to Estates Gazette.
It includes 46 Holiday Inn Express hotels and one Hampton by Hilton in Liverpool.
The sites are the first budget addition to London & Regional’s 15-strong high-end hotel portfolio, which includes the five-star London Hilton on Park Lane and Cliveden House in Berkshire.
Atlas Hotels – formerly Somerston Hotels – was acquired by Lone Star last year ahead of plans to grow the business to 60 sites over the next few years.
It also signed an agreement with InterContinental Hotels Group (IHG) to extend its franchise agreements by 15 years and develop at least 1,000 extra bedrooms by 2019.
Atlas is separate to Lone Star’s £1.5bn Amaris Hospitality hotel group, which includes the 31-strong Jurys Inn chain.