He said: "I am greatly fulfilled by the career I have had at the helm of the Ulster Branch but feel the time is now right for me to step down and pursue other interests.
"We have achieved a great deal in establishing a successful Ulster rugby brand, we have enjoyed Celtic and European success on the pitch and the game generally across the province is in a healthy state.
"I wish to thank the Officers and Committees of the Branch and Union for the opportunity to hold this position and for their support over the years, together with the staff for their help, their friendship and their continuing commitment to Ulster rugby.."
Cecil Watson, the President of the Ulster Branch, said: "On behalf of the Committee of the Ulster Branch, I wish to pay tribute to Michael Reid for the considerable contribution he has made to professional and domestic rugby in the province.
"Michael's commitment, dedication and expertise have enabled Ulster to achieve significant successes during a demanding transition to professional rugby.
"We thank him for all that Ulster achieved during his tenure and wish him well for the future.."
IRFU Chief Executive Philip Browne said: "Michael Reid has made a significant mark as a leading administrator in Ulster and Irish rugby.
"He pursued his duties as Ulster Branch CEO with great dedication over the challenging period as the professional game evolved and he can take great personal credit for the achievements of Ulster rugby, on and off the playing pitch."