He told the Ukrainian president: “On behalf of the Irish people, I wish to thank you for a defence of our shared international values.”
Ireland had welcomed many Ukrainian families, most of them women and children, seeking refuge from the “barbaric” war, he said, at the conclusion of a secret weekend trip to the war-torn country with Seanad Cathaoirleach Mark Daly.
Many of those who fled Ukraine had witnessed horrors that people in Ireland “can hardly comprehend”, the Ceann Comhairle added.
“I assure you today that those Ukrainians coming to our shores will be cared for with kindness, deep respect and dignity.”
Seanad Cathaoirleach Mr Daly said the Irish delegation had gained an invaluable insight into the war.
“The damage and impact on this beautiful country, both infrastructurally and psychologically, will take a long time to heal,” he said.
The group witnessed at first-hand the consequences of the occupation of the towns of Bucha and Irpin by Russian armed forces.
They saw the mass graves of civilians killed by the Russian occupiers in Bucha and then viewed the destruction caused by shelling and airstrikes of the residential area in Irpin.
Mr Daly said he invited his Ukrainian counterpart, Ruslan Stefanchuk, to speak in the Seanad in the near future.
Mr Daly and Mr Ó Fearghaíl also met Ukrainian prime minister Denys Shmyhal in Kyiv.
“This mission is an opportunity for Ireland to demonstrate its support for the Ukrainian people, its government and its parliament, which is continuing to function in spite of unimaginably difficult circumstances,” Mr Ó Fearghaíl said.
“Coming at a time when other countries are starting to reopen their embassies in Kyiv, this trip will be another symbol of normalisation.
“It is also an opportunity to highlight the distinct importance of our parliaments and their democratic resilience.”
Mr Daly added: “The fact that we have been invited is recognition by the Ukrainian government of the exceptional welcome extended by the people of Ireland to Ukrainian refugees and the assistance and funding that is being provided to those still in Ukraine.
“It’s crucial that Ireland plays a visible and vocal part in demonstrating EU support for Ukraine and for Ireland’s support for Ukraine’s membership of the EU.”
Mr Stefanchuk welcomed “support to our state at this difficult time of struggle against the aggressor”.
The delegation also visited some of the towns that have been decimated by the war and where atrocities have occurred, in order to highlight the need for those responsible to face justice for war crimes.
Last month Mr Zelensky made a historic address to the Dáil and Seanad via videolink, with refugees watching their president’s speech from the distinguished visitors’ gallery.
Mr Zelensky called on Ireland to convince the EU to impose even more sanctions on Russia and he thanked Ireland for the humanitarian support shown to refugees.
He also applauded Ireland for supporting Ukraine’s request to join the EU and asked the Government to convince “EU partners to introduce more rigid sanctions against Russia that would really make sure that the Russian war machine will stop”.