The League One club, who sacked Michael Collins on Monday night, have turned to the 48-year-old Scot as they look to usher in a period of stability.
Stuart McCall and Simon Grayson both left the club last season, while Collins only lasted six games of this campaign.
Hopkin, a Bradford player towards the end of his career, arrives with a good pedigree, having got Livingston to the Scottish Premiership last season.
Hopkin has signed a two-year-deal at Bradford, having opted to leave Livi despite securing back-to-back promotions.
“I am absolutely delighted to be joining the Bantams and cannot wait to get started,” he said.
“This is a huge opportunity for me. We have a talented squad and I am looking forward to working with the players and staff.”
Hopkin made 16 playing appearances for City in a career which also took in the likes of Leeds United, Chelsea, Crystal Palace and Morton.