Leanne Freeman had been found unconscious and bleeding from a gunshot wound to the head in the early morning hours of Nov. 29. She was found in the Port Lands, an isolated industrial area, and her clothes were found in a dumpster near where she was dumped on the road.
Jonathan Ash, 23, was arrested in December and initially charged with being an accessory after the fact to murder.
Police on Tuesday announced that "as a result of the ongoing investigation," that charge has now been upgraded to first-degree murder.
He is due to appear in court Wednesday morning.
Another man, Joseph Beauregard, 31, of Whitby, Ont., had also been arrested last December and was charged with first-degree murder.
Freeman, who was from Winnipeg but had been living in Toronto for several months, had been battling an addiction to crystal meth, according to her family and friends.