Born in Auckland on December 7 1988, Marshall played at fly-half in all 13 games for Tasman Makos during last ITM Cup, scoring three tries.
"When I found out that I missed Super 15 selection, my agent told me there was an opportunity over in Italy to play in the Magners League and Heineken Cup, so that was basically my reasoning behind it," said the 22-year-old.
Marshall said he was looking forward to simply improving his game.
"I wanted to try and develop my rugby, and I didn't think I'd be able to do that as well playing club rugby, so I wanted to be tested."
He said it would also be a perfect opportunity to work on his kicking game. "I'll try and work on that kicking game. It's going to be a pretty interesting experience, and should be a good chance to travel as well and see another part of the world.
"I've known kicking has been a weakness of mine for a while now, and this year was really the first year it's been found out. I think it's a good idea to be here and work on it. That'll be the main focus to work on while I'm with Aironi".
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland