“The decision to leave was extremely difficult but this is a fantastic opportunity to join one of the best clubs in Rugby League,” Solly said.
“It will be tough to leave a great group of people at the RFL and Super League, and I would like to thank the staff, clubs and fans for their support.
“The competition is in great shape, and in a strong position to grow quickly in the coming years. However the time is right to return with my family to Australia after over 11 years in the United Kingdom.
“I would also like to express my appreciation to the RFL for allowing me to begin work at South Sydney in May.”
RFL Chief Executive Nigel Wood said: “Blake has been an excellent General Manager for the First Utility Super League and we are all of course naturally disappointed that he is leaving to return to Australia.
“That said, we can fully understand the pull of leading one of the biggest clubs in Rugby League and returning home to Sydney.
“Over the last couple of years Blake has contributed an incredible amount to the RFL and in ensuring that the First Utility Super League remains the premier sports league of the British Summer. We wish him all the best in his new role.”
In the interim the RFL’s Marketing Director Mark Foster will take on the responsibilities of Super League General Manager while the RFL begin the search for a successor.
Foster who has been with the RFL for four years led on all marketing activity for the incredibly successful Rugby League World Cup 2013.