Liddle, who turns 28 on Sunday, has signed a one year deal with an extra year's option included to become the latest player to be added to Phil Parkinson's new-look squad for the forthcoming 2014/2015 season.
The Middlesbrough-born central midfielder, who can also play in defence, will officially join up with City on 1 July when his contract with Notts County expires.
He joins Matthew Dolan and Billy Knott on the Bantams' list of signings ahead of the return of pre-season training for the club next month.
Liddle actually played and scored for County against City at the Coral Windows Stadium last season during a 1-1 draw behind the two clubs back in November.
His appearance for County at Valley Parade in that game was one of over seventy he made for the Magpies during a two-year spell at Meadow Lane.
After penning his City contract, Liddle told Bantams Player: "Phil (Parkinson) rang me pretty soon after the news got out that I was leaving Notts County and I was delighted to see his name flash up on my phone.
"Straight after my meeting with him, I was speaking to my agent and my family telling them that this is the manager and this is the club I want to play for.
"As soon as the manager told me of his plans for next season, it was something I wanted to be a part of.
"Truth be told, there was the chance of me signing here for Bradford a couple of years ago, so to see the manager still interested in me now and still wanting to bring me to the club was fantastic."
Bantams boss Parkinson added: "I'm delighted with the arrival of Gary.
"He is a great professional, a good character, and a very versatile player.
"I feel he is going to be an important signing for us.
"We are still piecing things together for the new season, but Gary is another good addition to the squad."
A hugely popular performer during his time with County, the industrious midfielder helped to secure the Magpies' status in League 1 for next season despite the Nottingham club looking in serious danger of relegation on more than one occasion during the previous campaign.
Having played every second of County's league season during his first campaign at Meadow Lane - the 2012/2013 season - Liddle was also named the Magpies' Player of the Year for that year.
Before joining Notts County, Liddle spent six years at Hartlepool United, making nearly 250 appearances in the process.
Following Hartlepool's promotion into League 1 back in 2007, Liddle's combined playing experience with both County and Pools over recent years means the midfielder has spent his previous seven seasons at League 1 level.
Despite his long association with Hartlepool, Liddle actually started his career with home-town club Middlesbrough where he won the F.A Youth Cup back in 2004.