After completing the necessary paperwork this Monday, the talented West Ham United youngster will now remain with the Bantams until the start of January 2017.
The ball-playing central midfielder will certainly need no introduction to the vast majority of City supporters after a highly successful first loan spell with the club during the second half of last season.
Making his debut in City's 4-0 win at Peterborough United back in February, Cullen was on the losing side only four times in his seventeen games in Bradford colours, as the Bantams made the League One Play-Offs.
Speaking about his popular return to the Northern Commercials Stadium, Cullen said: "I really enjoyed my time at Bradford last season and it was a no-brainer really for me to return once I knew the club were interested in bringing me back.
"I am excited by the prospect of trying to push this club on again.
"Playing in the Play-Offs with Bradford and losing to Millwall in the semi-finals, it almost felt like unfinished business here for me.
"Obviously in the summer I didn't know exactly what my situation was going to be for this year but as soon as I knew West Ham were allowing me to come (to Bradford), I was straight in the car to get up here.
"The fans, players and the staff were all brilliant with me first time around and I feel really comfortable at the club.
"West Ham were really happy with the way Bradford treated me and Reece (Burke) last season. This is a great club and I am really happy to be back."
Cullen started in the official opening game for West Ham's new London Stadium against Juventus on Sunday, playing 83 minutes against the Italian champions.
He was also an unused substitute in both legs of the Hammers' recent UEFA Europa qualifying third round success over Slovenian side NK Domzale.
The midfielder will wear number 14 in his second spell with the football club.