Crowe, who bought a 75-percent stake in the century-old "Rabbitohs" with businessman Peter Holmes a Court in 2006, told Australia's Fairfax Media that he was trying to cut back on non-work commitments.
"If I have any chance of keeping my family together, I have to simplify my life where I can," Crowe said in an email.
Souths chairman Nick Pappas told a news conference that Crowe's decision to sell after the 2013 season was part of a "personal equation".
"He has a young family," he said, referring to Crowe's sons aged six and eight with his wife Danielle Spencer.
"It's a personal decision from him... and I think that we've got to respect that."
Crowe and Spencer separated after nine years of marriage last month.
Reports at the time said the demands of Crowe's acting career played a part in the split, with the star away for much of the past year filming "The Man with the Iron Fists", "Les Miserables", "Broken City", "Man of Steel" and "Noah".
The Oscar-winning star of "Gladiator" and "A Beautiful Mind" has been credited with helping to turn around the once-struggling Sydney side, which this season made it to the rugby league finals.
In a tweet, he said the club was "in a great place".
"Money in the bank, long-term contracts with star players, excellent coach. Don't listen to panic merchants," Crowe wrote.
Pappas said it would be up to Crowe to find a buyer for his share. It is not known what Holmes a Court is planning to do with his stake. The remaining 25 percent of the outfit is owned by South Sydney members.
Souths chief executive Shane Richardson said it was not the end for Crowe.
"Russell has the best interests of this club at heart. If it wasn't for Russell Crowe this club would not be here," he said.
The actor is credited with luring big-name players to the club, including Greg Inglis and English international Sam Burgess.
Born in New Zealand, Crowe has been a Rabbitohs fan since he moved to Australia as a child and regularly turns up to home games.