Majority shareholder Fawaz Al Hasawi will replace him in the key position at the City Ground.
Fawaz told the club's official website: "I would like to thank my cousin Omar for all the hard work he has put in since I took over the club in the summer.
"I'm looking forward to taking over as chairman and intend to spend even more time at the club. I'm sure we will continue to go from strength to strength."







