Packer has bought out Peter Holmes a Court's 37.5 per cent share in the Rabbitohs, to assume ownership with Crowe who took over following a membership vote in 2006.
The club's financial clout will now be unrivalled in Australian sport and rugby league's most popular club is set to challenge AFL giant Collingwood as the nation's most prominent sporting outfit.
A former board member with the Rabbitohs' bitter arch-rivals the Sydney Roosters, Packer happily confirmed over a year of speculation in a Rabbitohs media release.
"This is a very proud day for my family," Packer said in the statement.
"My father had a long history and association with Souths and to now be a co-owner with Russell Crowe and the members is an honour and a privilege.
"I am hopeful that working together with Russell, Souths Chairman Nick Pappas and CEO Shane Richardson, we can win more premierships for the fans, secure the club's long term financial future and in time establish Souths as Australia's number one football club; with the biggest supporter base for all codes.
"Can I put on record my gratitude to Peter Holmes a Court for the outstanding work he has done at Souths over many years and wish him well for the future."
The other 25 per cent of the club is owned by South Sydney Members Rugby League Football Club and the Rabbitohs statement said the new ownership structure would not affect the team's name, logo, colours, jersey and choice of home ground."
Rabbitohs chairman Nick Pappas said Packer's involvement with Souths ensures the club's long term viability.
Packer's casino venture Crown Resorts assumed the Rabbitohs major jumper sponsorship at the start of this year in a three-year deal.
"I join with the Rabbitohs' senior management team, our staff and our members in welcoming James Packer to the Rabbitohs family," Pappas said in the statement.
"We promised some years ago to deliver sustained on-field success and the first chapter of that story was written on 5 October 2014 with our 21st premiership.
"We also promised to connect our great club with the highest echelons of Australia's business community so that its longevity could be ensured for decades to come."
