Worthington has signed for the Bantams until the end of the season after being released from his contract by Oldham.
The 27-year-old said: "I'm happy to join Bradford and I want to fight for them to get them out of this position.
"It's time for us to roll up our sleeves, get stuck in and get climbing back up the table."
Worthington, born in Dewsbury, started his career at Huddersfield, where he made his debut as a 17-year-old in 2002 and went on to captain the side before his release in 2009 before joining Oldham.
Meanwhile, the Bantams have signed a new four-year deal with sportswear giant Nike to supply the club with their kit.