Weller, who joined Petrofac in September 2011 from Cable & Wireless Worldwide, is due to take up his new role with the security contractor after its current chief financial officer, Himanshu Raja, steps down on 1 October.
“I have thoroughly enjoyed my time at Petrofac and the decision to leave was not an easy one,” said Weller, who has been a non-executive director at G4S since April 2013.
“However, the opportunity to join G4S and an executive team that I have come to know and admire through my non-executive role with the company, is the right move for me at this time.”
Petrofac chief executive Ayman Asfari said the search for Weller’s successor is underway, adding: “On behalf of the board I would like to thank Tim for his significant contribution over the past five years. Over this time the group has gone through substantial strategic change and Tim’s experience, professionalism and measured approach have proven invaluable in helping us on our journey back to our traditional areas of focus.”
Ashley Almanza, chief executive of G4S, said: “Tim is a highly accomplished executive with extensive commercial and financial experience in global businesses. His experience and skill will be invaluable in leading our global finance team and supporting our broader transformation programme.”