Amid waves of thunderous applause from gathered MPs and senators, Prime Minister Stephen Harper welcomed Poroshenko, who lauded Canada for its unwavering support of Ukraine, not just in recent months but over the years as well.
Earlier this week, Poroshenko signed a co-operation agreement with the European Union that will deepen economic and political ties and help cement Ukraine's focus towards Europe and away from Russia.
"Yesterday was one of the most important days in the history of Ukraine … That was the last farewell from Ukraine to the Soviet Union," Poroshenko said, setting off another loud ovation.
"That was a Rubicon Ukraine crossed and we never, ever turn back to our awful past."
It was a decision last fall by former president Viktor Yanukovych to abandon an EU co-operation pact in favour of closer ties with Russia that sparked the popular uprising and plunged Ukraine into months of turmoil.
About 3,000 people have been killed, leaving the West and Russia — with Ukraine caught in the middle — mired in their worst crisis since the end of the Cold War.
Poroshenko was visibly moved even before he started his speech, putting his hand over his heart and mouthing the words "thank you" in the face of a standing ovation.
"I never feel anything like that," he said as he took the podium.
There are some 1.2 million people of Ukrainian descent in Canada and they form a powerful voting bloc in some key Toronto ridings as well as in communities across the Prairies.
Harper was the first western leader to visit Poroshenko, attending his inauguration in Kyiv in June. "This is not to us just a matter of international law or political principle," the prime minister said.
"This is matter of kinship; this is matter of family. This is personal, and we will stand by you."
As for the EU co-operation agreement, Poroshenko said not only will it harmonize Ukraine's trade and customs structure with Europe, it will bring it closer to the western world, economically and politically.
He branded the struggle with Russian-backed rebels in the east of his country as "a war against terror" and said Ukraine is united with its western allies to end the violence and live in peace.
"With your support, the support of the global community, we will win this struggle. And we will fulfil the dreams of many Ukrainians in our homeland and across the world — Ukraine will be strong and independent, (a) very important European nation."
For his part, Harper pledged the support of all Canadians, across party lines, for Ukraine's fight for freedom from Russian aggression "whether it takes five months or 50 years."
EU member Denmark welcomed the new economic co-operation pact with Ukraine and said more sanctions against Russia could be in offing.
"Ukraine, with this, sends a clear signal that they belong to Europe and they want a strong relation with the European Union," Danish Trade Minister Mogens Jensen said Wednesday during a separate visit to Ottawa.
Jensen said Europe and the world must send "a strong signal to Russia because they are endangering not only eastern Europe but world peace by having such an aggressive approach to neighbouring countries."
Poroshenko also spoke of the possibilities of a future that would bring deeper co-operation with Canada in trade, energy, investment and aerospace. He said he hoped to see a Ukraine-Canada free trade agreement.
Earlier Wednesday, Harper and the Ukrainian leader exchanged warm greetings and affirmed their mutual solidarity and support in brief remarks, after Harper gave Poroshenko a red-carpet welcome to the Centre Block.
"I know it's a very difficult time and we're greatly honoured that you were able to share this time with us on your visit to North America and to give us the opportunity to express our support for your government," Harper told his visitor during a photo opportunity in his office.
A nearly two-week-old cease fire is holding in Ukraine, but tension continues between government forces and Russian-backed rebels in the east. A building in Donetsk was hit by rocket fire today, killing at least one person.
The Harper government has been a fierce critic of Russian President Vladimir Putin, joining an international sanctions effort. Harper has blamed Putin personally for threatening world peace by provoking the unrest in eastern Ukraine and annexing the Crimean peninsula.