Const. David Cavanagh was originally charged with manslaughter in the death of Eric Osawe, a Toronto man, who was shot during a police search on Sept. 29, 2010.
The charge was subsequently upgraded to second-degree murder in 2012.
Earlier this year, a judge at a preliminary inquiry decided there wasn't enough evidence to commit Cavanagh to trial on the charge. The case was then dismissed.
The Crown appealed that judge's decision, seeking to send Cavanagh to trial on the manslaughter charge he originally faced.
But an Ontario Superior Court judge dismissed that appeal on Thursday, ruling that Cavanagh’s weapon was accidentally discharged during a struggle with Osawe.