The 6ft 2 player who weighs 120kg and wears a 2XL, said he was a good fit for the brand because their clothes were made for bigger guys like himself.
"Its normally pretty tough getting pants and that to fit around the butt and thighs. That's probably one of the big plus sides of Johnny Bigg is that their stuff actually fits really well," said Moody.
Moody said his role as an ambassador has involved taking photos of himself in the gear and posting them to social media.
The regular starter for the All Blacks stopped wearing a sling, used to support his injured shoulder, last weekend.
"That's one big tick and a positive step forward. But there's a long way to go yet." he said.
"It's still very stiff and I don't have a lot of movement back in my shoulder yet, so I'm doing a range of motion stuff trying to get it back moving again."
The first New Zealand Johnny Bigg store was set to open at Westfield Manukau City on November 21.