The 22-year-old former Liverpool trainee has signed a three-and-a-half-year deal with the Molineux club.
Hammill, who has also had spells with Dunfermline, Southampton and Blackpool, has been Barnsley`s stand-out performer this season, netting eight goals for the Championship club.
"Wolves are a massive club and I'm looking forward to playing my part for the rest of the season," Hammill told Wolves' official website, www.wolves.co.uk.
"I'm pleased to be getting the chance to try and play Premier League football. My agent has got a few players here already and they all say how much they enjoy playing under Mick McCarthy and the staff here.
"It seems a really good working environment and I can't wait to get going and get the shirt on.
"I think my ambitions go hand in hand with the club.
"I'm really keen to play in the Premier League and the club are keen to establish themselves here and I'm really excited about the prospect."
Source: PA
Source: PA