Councillor Keith Barrow was found by a standards sub-committee to have broken the council's rules by failing to disclose a personal and business relationship with a director of the company eventually appointed as accountants and auditors of Shropshire Council company ip&e.
The Conservative councillor said he had not voted on the matter and apologised for breaking the rules.
He said: "I wish to apologise for failing to formally declare matters. I accept the informal declaration I made after the appointment was made by colleagues should have been recorded in writing thereafter.
"I am extremely grateful to councillors and council officers for the unstinting support I have received whilst this was investigated independently and for their co-operation with both the independent investigator and my solicitor to ensure all the evidence was gathered which was relevant; including that which supported my recollection."
Councillor Barrow, who will now undergo code of conduct training, said the verdict had confirmed that he not exercised any undue influence.
He said: "The existence of a detailed, independent and legally-led process which confirms that no undue influence occurred is welcome.
"As the report confirms, the selection process for accountants and auditors was managed by the then chief executive. The process followed was independent, objective and lead to procurement on merit alone.
"As chairman of any committee or board it is my long stranding policy not to vote or influence the outcome unless a casting vote is required from the chairman. In this case no casting vote was needed so colleagues quite properly accepted the objective recommendation of the then chief executive.
"This error was a good faith oversight on my part. Neither I nor anyone else benefitted from this oversight."