Edelman won a multi-agency pitch, revealed by prweek.com/uk, on 9 December, with a number of international corporate and financial agencies taking part.
The brief is thought to be group-wide across Europe, designed to help unify the firm's corporate messaging across the region.
Rolls-Royce uses Brunswick for financial PR in the UK, which is thought to be unaffected by Edelman's hire.
Rolls-Royce's international reputation took a big blow last November after problems with its Trent 900 engine, which forced an emergency landing of a Qantas plane in Singapore.
Earlier this month, Rolls-Royce revealed that the Qantas incident had resulted in a £56m dent to full-year profits.
Civil aerospace is understood to be a crucial aspect of the brief, but the account is believed to include Rolls-Royce's defence aerospace, marine, energy, nuclear and services divisions.
Rolls-Royce was unavailable for comment and Edelman declined to comment.
The in-house comms team at Rolls-Royce is led by corporate affairs director Peter Morgan, who joined near the end of 2009 from his role as group director of comms for BT.