Aron Firman, 27, who suffered from schizophrenia, was shocked by an Ontario provincial police officer when he became combative after officers tried to arrest him, the Canadian Broadcasting Corp. reported Tuesday.
The medical examiner ruled Firman died of heart failure.
Ontario's Special Investigative Unit concluded that the use of the stun gun caused Firman's death but said there were "no reasonable grounds" to charge the officer who used the weapon.
"In these circumstances, and in light of Mr. Firman's demonstrated degree of aggression, I am of the opinion that the Taser's deployment was not excessive, notwithstanding the fact that it caused Mr. Firman's demise," SIU Director Ian Scott said.
Firman's is only the second case in Canada where a medical examiner has blamed an electrical stun gun for sparking heart failure.