Following a highly successful first spell on loan with the Bantams last season, Cullen returned to the Northern Commercials Stadium on Monday after his parent club West Ham United gave City the green light to borrow the talented midfielder once again.
Cullen has penned a five-month deal, keeping him at Valley Parade until the start of January 2017.
McCall said: "I think everyone knows that midfield is an area that we have been looking to strengthen and we targeted Josh from almost the minute we came in.
"I watched him plenty of times last season and I saw him play very well for 83 minutes for West Ham against a strong Juventus side on Sunday.
"Good work from a lot of people behind the scenes has made this deal happen. He will come in and add good competition to midfield, an area which I feel we are now looking strong in.
"It will be a fight for Josh to get into the side but I'm sure he's relishing it.
"He's not just a sitting midfielder, he can get forward well. He has good quality and good energy.
"He knows the place well from last season so there won't be a massive upheaval for him. He enjoyed his time with the fans and the players last time and I think that has definitely played a part in his decision to come back.
"He was fantastic for the club last season and we hope he can be as success again for us this year."