It found that he was never a member of the Special Air Service Regiment and had only ever served briefly in the army reserves.
The CCC also found no evidence to back Mr Thompson's claims he had two university degrees and suffered from oesophageal cancer.
During his first election campaign, Mr Thompson claimed to be a cancer survivor in election materials.
"Mr Thompson's cancer claims have varied; however, his more expansive commentary has been in relation to suffering from oesophageal cancer," the CCC's report states.
"The CCC obtained copies of Mr Thompson's medical records — none of which record a diagnosis of oesophageal cancer or treatment for the same beyond Mr Thompson's own self-reports."
Instead, the records show his only brush with cancer was having minor skin cancers removed.
The investigation also found evidence that as mayor, Mr Thompson shared confidential and commercially sensitive council documents to an unauthorised external adviser.
Mr Thompson won the mayoralty in March 2024 largely after claiming to have served in the army for five years, including at Swanbourne, the elite Special Air Service base in Western Australia.
After questions were raised about his service, Mr Thompson said he had in fact served three years in the Army Reserve, mostly in catering.
He blamed a history of "100-plus" concussions for his confusion over the matter.
He formally resigned in September after being suspended for 12 months on full pay by the Queensland government in November 2024 before losing a subsequent by-election.
Mr Thompson declined to be interviewed by the CCC during the investigation and "denies committing any kind of misconduct or criminal offence and respectfully declines to provide a response in circumstances where there is the prospect of future criminal proceedings'.
While the CCC did not result in criminal charges, the watchdog has called for reforms to ensure truthful conduct by candidates.
Recommendations include introducing a mechanism for candidates to declare qualifications and employment history, with a sanction for providing false information and a review of whether further regulation is required around private advisers.
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