Hawley, 31, signed a short-term deal under former Iron boss Alan Knill in early September following his release by Notts County at the end of last season and that was scheduled to expire after Saturday's home draw with Shrewsbury.
"Karl's been a very, very good player for us," manager Brian Laws told the club's official website. "People might look and say he hasn't scored a great deal of goals, but he has contributed with goals and also had a big contribution with assists as well.
"He's been a good player for us and we're delighted we've agreed terms with him. Hopefully he will help us no end to push on."
The former Carlisle forward has scored five goals in 21 appearances for the Iron this season.