Sandra Bergen, 23, suffered a heart attack and spent 11 days in a coma after taking crystal methamphetamine.
Ms Bergen said Clinton Davey had known the drug was highly addictive and dangerous but sold it to make money.
Mr Davey refused to name his source of the drug, prompting the Saskatchewan judge to reject his defence - that Ms Bergen had taken the drug voluntarily.
'Hit drug dealers'
Ms Bergen is seeking $50,000 (£25,000) in compensation. A date for a hearing to determine damages has not been set.
"I sued him for negligence... for selling me drugs and getting me hooked when I was vulnerable," Ms Bergen told the French news agency AFP.
She said she hoped her case would inspire others to sue drug dealers.
"I think it's a different way to hit drug dealers financially and that's where it will really hurt them," she told CTV news.
Ms Bergen and Mr Davey were friends from childhood.
In her statement of claim, she said he "knew the drug was highly addictive" and that his dealing was not only "for the purpose of making money but was also for the purpose of intentionally inflicting physical and mental suffering" on her.
In his defence, Mr Davey had argued that Ms Bergen "voluntarily consumed illegal drugs, thus contributing to her own condition."
"She assumed the risks," he said.
Ms Bergen became addicted to drugs when she was 18, CTV news said. She overdosed in 2004 in the province of Saskatchewan shortly before her 20th birthday.
In hospital she was hooked up to a respirator. She said she suffered lung, heart, kidney and liver failure and may never be able to have children.
She said she has since stopped taking drugs.