Warnock announced his retirement from the dugouts in April last year, five months after leaving Middlesbrough.
The 74-year-old holds the record as the manager with most promotions in English football with eight, including three promotions to the Premier League with Sheffield United, Queens Park Rangers and Cardiff City.
Huddersfield are stuck in the Championship relegation zone, with just seven wins all season and one point from safety.
The Terriers recently sacked manager Mark Fotheringham.
This will be the second time Warnock will be managing Huddersfield Town, with his first spell coming almost 30 years ago.
"I'm really excited about this challenge," Warnock told Huddersfield's official website.
"My first spell at Huddersfield Town had everything; we went to Wembley twice, moved into the new stadium, and really built the club from nothing. It was a special time.
"I'm coming back to help the club, but also [chairman] Dean Hoyle. I know what he has done behind the scenes and I've always had a lot of time for him.
"I've looked at the fixtures and we've got some fantastic games to come. I want to come back and put smiles on faces."
