White will move from New Zealand to join Bristol in February before taking over from Portch at the end of June. Portch took over in 2003 when a local consortium assumed control of the club after relegation.
"I am delighted that the consortium has asked me to remain with the club as an executive director with special responsibilities," Portch told the BBC. "I would like to express my thanks to the staff who have worked so hard, to the volunteers, including former players, and to Richard Hill and the squad, who have been totally supportive."
White is a former international cricketer who spent five years with Auckland and the Blues Super 14 franchise. "There is a lot for administrators to gain from having a broader perspective on the game," he added.
