Dieng has put pen to paper on a two-year deal at Valley Parade to become City's fourth signing of the summer.
The highly-rated 24 year-old, who is comfortable in both midfield and defence, has been involved in pre-season training with McCall's men for the past week.
He also featured for the Bantams in their opening friendly at Guiseley last weekend, hitting the bar with a powerful strike from outside the area.
After confirming his move to the Bantams, Dieng said: "I know that Bradford is a big club, an ambitious club, with a lot of fans and a great stadium.
"I am looking forward to playing in front of the fans and in this great atmosphere.
"I met the players last week when I first came here to train and they are a good group. They have helped me to settle in.
"I've already had two years in England and this has helped me to understand the language and adapt to the English game."
The Frenchman already has experience of playing in Sky Bet League One having played a sizeable role in helping Oldham to defy the odds and retain their status in the division last season.
Dieng spent two seasons in total with Oldham, making 68 appearances in all competitions, after joining the Latics in July 2014.
He began his professional career in his native France with former Ligue 1 side Brest, spending three years with the club.