The motion, which described Yellowknife as a "city for peace," passed by a vote of 6 to 1.
Outside the chambers, 20 people held a vigil for victims of the Iraq war, and asked council to support their motion as they entered City Hall.
Yellowknife resident Chris Inkster spoke inside asking councillors to support a motion condemning unilateral military action and lauding the federal government's respect of the United Nations.
Inkster, who was accompanied by a dozen supporters in the gallery, said he was disappointed that council voted down a similar motion three weeks ago.
He said council has a responsibility to be a voice for its constituents.
"You argued that council doesn't have jurisdiction in this area," he said. "I'm concerned by that argument. It's a veiled argument against democracy itself."
Inkster said the message of peace is still relevant despite the war in Iraq winding down.
"The U.S. administration is now discussing pre-emptive means to attack Syria," he said. "I don't think this is over."
Coun. David McCann was the only member to vote against the motion, citing his lack of faith in the efficiency of the United Nations and reiterating that he doesn't believe foreign policy debates belong in the council chambers.
"This distracts us from our core business, which is providing services to our residents," he said. "There's already a vehicle for these concerns in the Government of Canada."
Mayor Gord Van Tighem thanked Inkster and his supporters when the motion passed.
"I congratulate them for being persistent."