Edel McCaffrey will join the company in mid-April, reporting to group director of comms Matt Peacock.
'BG Group is growing rapidly and is one of the most dynamic companies in a complex sector,' said McCaffrey.
She has been based at the company's corporate headquarters for over four years, working on protecting its external reputation. She currently reports to AZ V-P group corporate comms Caroline Hempstead.
Before joining AZ's corporate affairs department, McCaffrey was based in its UK marketing company for three years.
Previously, she spent two years as a consultant at PR agency GCI Group.
McCaffrey's departure follows the exit of AZ's top communicator Sally Sykes to join Johnson & Johnson earlier this month (PRWeek, 8 February ).