The report had been expected in the next month or so, but is now due before Oct. 31, 2014.
The provincial government granted the extension for the report at the request of Commissioner Paul Belanger.
The commissioner cited the length and complexity of the hearings and round tables of experts, along with having to sort and analyze a large volume of materials.
In granting the extension, the province said it still expected the inquiry to come in on a budget of $20 million.
The inquiry, which wrapped up hearings in the fall, has been examining the collapse of the mall in Elliot Lake, Ont., in June 2012 in which two women were killed.