Cairns, 37, who retired from international cricket last year, told the Christchurch Press newspaper he had accepted a "lucrative" offer to play in the inaugural Twenty20 competition, due to start in November.
"It's a lucrative deal," Cairns said. "It's something which has brought me out of retirement and to do that it has to be worth it.
"The competition is also a chance to have one last go playing in front of heaps of people."
Cairns joins former New Zealand internationals Chris Harris, Nathan Astle and Hamish Marshall in the competition, which is due to run for about five weeks beginning Nov. 17.
"I've had mixed emotions over it. It's such a good offer that I thought I will have to train again. I thought I'd finished with that garbage," he said.
"I'd done it for so long and thought 'I can now kick back' but now I have to get serious because I want to acquit myself professionally."