The two appointments are a result of Gallot's decision to move on after 11 years.
Gregan started his career in New Zealand's wine industry fresh out of university in 1983.
Geary has been interim CEO for the last two months.
Gregor has been a non-executive director at the company for the last year.
The changes will be applied across South Africa's export markets from next year.
Diageo chair Sir John Manzoni said Rishton brings 'a track record of creating sustainable, long-term…
