He has joined the West Yorkshire club on a one-year deal with the option for a second.
Whitbread, 23, made 30 appearances for Gold Coast Titans in the NRL before switching to Super League with Leigh towards the end of last season.
Having started training with Willie Poching’s side, he said: “It’s been unreal so far – the lads have been very welcoming and I’m enjoying being in training.
“My time at Leigh has given me an insight into what I can expect playing in Super League and I’m really looking forward to it.
“It’s a high-paced game, there are plenty of offloads and the ball is always in play.
“It’s a really enjoyable brand of footy to play and watch, so I’m just ready to get ripped in now and can’t wait for it.”
Poching added: “It’s not often you get someone of Jai’s NRL experience and age on our doorstep.
“So, when the chance came to meet and speak to him, I was taken by his demeanour, size and his will to keep developing and have a big impact on our team and club.
“He is a good young man, who as a player has a great skill set for a big fella, and he will complement and enhance the style we want to implement next season.”