"I'm delighted, it's great to be back at the club." said the striker.
Thomas, who had a previous spell at St. Andrew's on loan from AFC Bournemouth during the 2012/13 campaign impressed manager Lee Clark during his stint at the club - which saw the forward net three times in eleven appearances.
Thomas told BluesTV: "I want to play as many games as possible, score as many goals as possible and hopefully we can have a very good season."
Check out the full interview with Wes below: