Redman said not achieving on-field success has been deeply frustrating but he leaves the club having helped assemble a coaching group as good as any in Super Rugby with world class support staff.
"Now we have just signed one of the best players in the world. We have fantastic staff and I know success is just around the corner."
Board Chair Don Mackinnon thanked Redman for his six years of dedicated, professional leadership.
"Despite facing numerous challenges, Michael has managed to grow our commercial revenue and oversee our move to a stunning facility that will set the Club up for decades to come. He has developed a strong team, worked incredibly hard and has led with integrity and intelligence. We thank him for all he has done. Michael will always be part of the Blues family."
New Zealand Rugby chief executive Steve Tew praised Redman for his contribution to the Blues and NZ Rugby.
"Michael can be very satisfied with what he has achieved at the Blues having steered the organisation through some challenging periods as it matured into an independent Super Rugby club.
"He has made significant contributions to rugby from his work on Collective Employment Agreements, to innovations in commercial and player contracting, and establishing a world class base for the Club at Epsom. That base, which sees the commercial and administration team working alongside the High-Performance group, coaches and team, has helped to underline a strong Blues culture and identity.
"While we hope Michael is not completely lost to rugby, we wish him well in his next ventures."
Redman will leave the club in September after completing the 2019 season review and the 2020 budget.
"The big rocks are in place for next season both on and off the field. We have some exciting announcements regarding our 2020 draw and Auckland Rugby are using our training facility starting in a few weeks. So, someone can come in and have time to get their feet under the desk."
Redman acknowledged the leadership of former and current chairs Tony Carter and Don Mackinnon.
"I have been very fortunate to work for two outstanding Chairs in Tony and Don and I thank them sincerely for their support and advice over the years.
"I will always be a Blues fan."
Mackinnon confirmed the process to recruit a new CEO would begin immediately.