The hospital trust released a statement on Monday confirming Mr Maclean's shock resignation last Friday - two months after its Council of Governors launched an independent inquiry into the unexpected absence of chief executive Ed Donald.
The trust insists Mr Donald, who left his post for three weeks in December, was on annual leave, but it is believed he himself quit after a vote of no confidence when a heated management meeting exposed a rift with Mr Maclean.
Mr Maclean, who declared himself "proud" of the hospital's achievements under his 12 years of leadership, was due to retire later this year anyway, so the trust had already begun a search for his replacement.
Reading East MP Rob Wilson, who hailed Mr Maclean as a "key figure" in the hospital's management, said he was "disappointed" by the resignation and added: "I hope they have someone in mind ready to step in. It's crucial they get someone with the right calibre and experience who will continue his work and take the trust forward. I will be very concerned if the trust went for any period of time without a chairman."
Reading Borough Council leader Jo Lovelock said: "It's important a new chairman is appointed as soon as possible. Colin had put in a huge amount of work over the years and I wish him well."
Mr Maclean, who was instrumental in establishing the hospital's foundation trust status in 2006, praised staff for their "can do" attitude.
and added: "The trust has been an initiator of new treatments and techniques and has a reputation for winning national prizes and accolades. It's been a privilege to have worked with such people and I wish them all well in the future."
Former Reading Mayor and Redlands ward Labour election candidate Tony Jones hopes it signals a "fresh start" and wrote on his blog on Sunday : "Hopefully this draws a line under an unhappy period at the hospital. However, this cannot be taken for granted as the attitudes of the remaining non executive directors is unclear."