Carol Bellringer's annual report says the improper payments were made between 2007 and 2011 to five high-ranking officials.
None of them is still with the office.
Bellringer was asked to investigate after government auditors examined the fire commission's books in 2011.
She says the coverup resorted to forgery in one instance.
Bellringer is recommending that the Finance Department forward her findings to the government's civil legal services.
She also suggests Manitoba's whistleblower legislation may need to be revised to ensure that the "control environment in government is functioning as intended."
"The blame must be placed on the individuals directly involved in the financial irregularities," Bellringer wrote in her report released Wednesday.
"But it is important to analyze what went wrong in the system to permit this to take place."
Bellringer, who examined thousands of records and individual transactions, said the payouts were made in a number of ways.
"Many payments were for personal expenses, amounts were claimed on more than one occasion and, in a number of instances, payments were made with no supporting documentation at all," she wrote.
Some payments were supported with manipulated receipts that had details of the items purchased torn off.
The office wasn't following its own or government policies for travel-related expenses either, she said.
Fire commissioner Christopher Jones, the office's deputy commissioner and another employee were all sacked by the government in 2011 after the provincial probe.
(CJOB, The Canadian Press)