The $175 million project was a commercial venture involving 300 homes and shops with a Queen St frontage.
However, one of Relianz' founders had a degree in piano performance from Auckland University's music school.
"So there is a real passion for the performing arts, which is the driver to reopen Auckland's once premier performing arts venue."
Former owner Paul Doole bought the theatre complex in 2002 and in 2009 won resource consent for the 39-level apartment tower and retail development.
Mr Gibbon said Relianz would work jointly with the Auckland Notable Properties Trust. The privately funded trust's principal, Steve Bielby, said its main concern was restoring the St James Theatre and the cost of it would be known after six to nine months of detailed assessment.
Restoration had previously been estimated at $50 million.
The reopening would be after all safety and earthquake strengthening work was done, but the whole project could be finished in 2018.
Heritage New Zealand general manager Sherry Reynolds was delighted to learn about the joint project.
The theatre was opened in 1928 and was on Heritage New Zealand's national list as a Category 1 significant historic place and was unique.
Auckland Mayor Len Brown said Auckland ratepayers would be pleased that private enterprise was creating an opportunity for restoration, which the public had said was a high priority.
The St James Saviours' campaign to save the theatre began six years ago and two years ago Bob Kerridge formed the St James Charitable Trust. "We are excited there is opportunity for St James to come back in its former glory," he said.