Vasyl Myroshnychenko joined 150 people outside the Russian embassy in Canberra on Saturday, one in a string of gatherings planned across the country ahead of the war's anniversary date on February 24.
Mr Myroshnychenko said he was hopeful for the conflict's eventual resolution.
"I feel optimistic. I'm hoping, I'm convinced history is on our side. It's clear who's evil and we are fighting for our survival," he told AAP.
"We are David fighting Goliath and it's pretty clear for me that's what gives me strength, because I believe Australians understand it."
The crowds were joined by Independent Senator David Pocock as some waved Ukraine and Australian flags while others held signs painted with 'stop war' slogans.
Australia has sharply differed from the US on how peace should be achieved in Ukraine after Donald Trump launched a scathing attack on its leader Volodymyr Zelenskiy.
Mr Trump trashed the Ukrainian president as a "dictator without elections" and falsely claimed Kyiv had "started" the Russian war before backtracking on his comments.
The US president incorrectly stated Mr Zelenskiy's approval rating was down to four per cent and implied Ukraine had stolen billions of dollars from his country.
Mr Myroshnychenko said Australia must band together with countries elsewhere to ensure support for Ukraine in its conflict.
"This is what we are now working on now, you know we want peace more than anybody else," he said.
"What we want to avoid, we want to avoid a brief break that will enable Russia to resupply, regroup and launch another attack.
"For us, security guarantees are a must, and we must figure out a way how we get those security guarantees."
In a strong rebuke this week, Opposition Leader Peter Dutton said Australia needed to back Ukraine.
"The thought that President Zelenskiy or the Ukrainian people started this battle, or somehow they were responsible for the war, is just wrong," he told 2GB Sydney.
"But Australia should stand strong and proud with the people of Ukraine. It's a democracy, and this is a fight for civilisation.
"Vladimir Putin is a murderous dictator and we shouldn't be giving him an inch."
Prime Minister Anthony Albanese reaffirmed the nation's support.
"Australia stands with Ukraine in their struggle, which is a struggle not just for their own national sovereignty, but it's the struggle to stand up for the international rule of law," he told reporters in Whyalla on Thursday.
Australia has committed more than $1.5 billion in aid to Ukraine since Russia's invasion on February 24, 2022.
To mark the anniversary, a charity concert was held in Melbourne's CBD on Saturday night while crowds gathered in a separate demonstration at Parliament Lawns in Hobart.
NSW Premier Chris Minns will attend a service St Mary's Cathedral Square on Monday evening.
Earlier in the day, the Ukrainian Community Centre in Adelaide's Hindmarsh will hold a service and crowds will again gather at the Russian Embassy in Canberra.
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