The central defender scored seven times last term but had drawn a blank until netting in the 2-0 win over Everton last month.
Cahill joined Wanderers from Villa in 2008 and has gone from strength to strength, recently establishing himself in the England squad.
The 25-year-old told the club's official website: "Steve Davis, the coach at the club, kept telling me throughout this season that the goals will come. I always knew that it would but it was taking far too long.
"So for me to get that scrappy goal against Everton was just what I needed. When you get a couple you have the belief that you are going to score every time that you go up the field.
"I hope it continues and that I can contribute with a few more goals from now until the end of the season because there is a big spell coming up for the football club."