Gordon Matheson faced claims he tried to pressure officials into supporting his favourite design and broke the councillors' code of conduct by failing to chair the judging panel impartially. But in a ruling yesterday, Scotland's standards watchdog threw out both complaints.
Dr Stuart Allan, the Commissioner for Ethical Standards in Public Life, said no further action would be taken.
The complaints followed the council's controversial decision not to proceed with the winning design, by architects John McAslan and Partners, to revamp the city landmark.
Instead councillors abandoned the £15 million proposals and announced a scaled back, £500,000 facelift, claiming there was little public support for any of the competition entries.
Amid anger among some architects, professional body the Royal Incorporation of Architects in Scotland lodged an official complaint about Mr Matheson's conduct as chairman of the judging panel. It accused him of trying to "coerce" two council officials involved in the judging process to support his own favourite design.
Dr Allan said there was no evidence to support the claim and suggested such a plan would not have swayed the renowned judging panel.
On the second allegation, the watchdog's probe found that Mr Matheson told a judging panel meeting that of the anonymous entries he preferred "submission six" and disliked "submission two", before leaving early for another engagement.
Dr Allan found he was entitled to express a view and had judged the entries fairly. He also stated that Mr Matheson had a duty "to have regard to the emerging weight of public opinion as to the redesign of George Square ".
Work on the scaled-down redevelopment is now under way and will be complete in time for the start of next year's Commonwealth Games.