The country's highest court said Friday it had dismissed Tony Accurso's request with costs.
Accurso, once the owner of several influential Quebec construction companies, has been trying to avoid testifying before the Charbonneau Commission, the province's corruption inquiry.
He wanted permission from the high court to argue his case for exemption before them.
Accurso, whose name has surfaced repeatedly during inquiry hearings, has now exhausted every legal recourse to get a summons annulled.
Barring any other challenges, Accurso is scheduled to testify for four days beginning on Sept. 2
Accurso had argued unsuccessfully in lower courts that testifying at the inquiry could jeopardize his right to a fair trial in pending criminal proceedings.
He is facing charges in several high-profile municipal corruption cases and is also charged with alleged tax fraud.
Quebec Superior Court and the Quebec Court of Appeal had already ruled against Accurso, who then petitioned the highest court in the land to rule on his case.
As is the high court's custom, no reason was given for its decision not to hear Accurso.
In May, Quebec Superior Court dismissed his initial motion for a judicial review where he argued the summons should be cancelled. That court ruled that Accurso had failed to demonstrate that his constitutional rights would be violated by being compelled to testify.
In June, the Quebec Court of Appeal refused to allow him leave to appeal the Superior Court judgment, noting that the Charbonneau Commission has promised to stay away from the criminal charges in its questioning.
Quebec Court of Appeal Justice Francois Doyon wrote he has no doubt the province's Superior Court would intervene to protect Accurso's rights if that promise was not kept.
The high-profile corruption inquiry, which is studying the construction industry and the awarding and management of public contracts, resumes Aug. 25.
The inquiry has already heard from more than 100 witnesses since it came into existence in 2011 and Accurso is expected to be among a final group before it moves into a consultation phase in the fall.
The inquiry, co-chaired by Justice France Charbonneau and former provincial auditor general Renaud Lachance, is expected to publish its final report by April 2015.