OneBeacon Insurance Group has appointed Dennis Crosby as president of the Canton-based company’s newest business, Excess and Surplus Lines.

The insurer established the group to support its current business as well as write in the E&S market.

Crosby was most recently president and CEO of ACE Westchester and chairman of ACE Commercial Risk Services, where he was accountable for wholesale distribution of specialized property and casualty products within the excess and surplus lines marketplace.

Prior to his six years at ACE, he worked with St. Paul Travelers for 23 years in a variety of roles, including commercial middle market, insurance operations and public sector services.