ROSWELL, Ga.—ACE Group of Cos. Ltd. on Thursday promoted Bruce Kessler to president of ACE Westchester.

Mr. Kessler oversees all operations of the Roswell, Ga.-based excess and surplus lines unit, including property/casualty, environmental, professional liability and inland marine products, the insurer said in a statement.

He succeeds Dennis Crosby, who now is president of the newly established E&S unit of OneBeacon Group Ltd., according to a separate statement.

Mr. Kessler has held various senior management posts at ACE, most recently as president of ACE Westchester’s casualty and specialty lines.