Smith, 20, made 24 appearances for the Rabbitohs Under 20s team last season, and is a former Castleford Lock Lane amateur.
He said: “I’m really excited. It’s a big opportunity for me and I’m going to grab it with both hands.
“I spoke to Richard (Agar) and he said there would be a big opportunity here and that’s what I want.
“Australia was the best experience of my life. It’s changed me massively on and off the field. Mostly off the field and I’ve turned into a man, as they say. Australia’s a great country and I loved it out there.
“I’m really looking forward to ripping in and getting a Wakefield jersey on. I’m just looking to try and establish myself over here and do my best for Wakefield.”