The Taoiseach said he is confident that Ireland's interests will be reflected in the draft Brexit negotiating guidelines due to be published by Brussels on Friday.
With the formal divorce process now underway, European Council President Donald Tusk will set out the bloc's priorities for the talks, which the Government expects will make reference to Ireland's "unique circumstances", including the pledge that there will be no return to a hard border.
It comes as the chairman of the European People's Party (EPP) Group in the European Parliament said the remaining EU member states are "united" in defending Ireland's interests in the Brexit talks.
Speaking in Malta, on the margins of the EPP Congress, Mr Kenny described today as an "unprecedented" day, and warned the negotiations would not be easy.
"It will be very challenging and very complicated," Mr Kenny said.
The Taoiseach said he was glad to see Ireland's priorities reflected in the Article 50 letter delivered earlier today by Britain's ambassador to the EU to Mr Tusk.
In it, Prime Minister Theresa May said Britain must pay attention to its "unique relationship" with the Republic of Ireland, and the importance of the peace process.
"The Republic of Ireland is the only EU member state with a land border with the United Kingdom," the letter stated.
"We want to avoid a return to a hard border between our two countries, to be able to maintain the Common Travel Area between us, and to make sure that the UK's withdrawal from the EU does not harm the Republic of Ireland."
Mr Kenny said his immediate focus was to ensure those priorities are included in Europe's negotiating position, which is due to signed off by European leaders at a special summit on April 29.
"I am confident that the principles and the priorities that have been set out here in respect of Ireland's position, our trading relationship with Britain, the Good Friday Agreement, the peace process, no return to a hard border, these matters will be reflected in the document that will be circulated on Friday from the European Council," Mr Kenny said.
But nine months on from the referendum vote, and with the formal exit process now underway, there is little clarity as to how a toughening of the border on the island can be avoid - especially if the UK ends up outside of the customs union.
Mr Kenny described it as a "political challenge", but reiterated that there should be no physical customs posts.
"It will require both imagination and creativity to deal with the outcome of that. We didn't cause this, but we have to deal with the reality of the consequences of it. So that's part of the central negotiations that will apply in the context of the Irish position.
It will be very challenging and very complicated. Taoiseach Enda Kenny
"Obviously, the trading relationships between the United Kingdom and the European Union are critical issues and I think that these will run a lot longer than the two year period, but central to that will be no return to a hard border as the only land border within the European Union."
Earlier, Manfred Weber, the chair of the EPP group in the European Parliament, said the Good Friday Agreement needs to be protected, and that Ireland's interests will be defended by Europe.
"For Ireland it is extremely important to say, you are not alone," the German MEP said.
"The Irish citizens need to know that they are backed by [the remaining] member states. The other partners are united in defending the Irish interests in regard to London's position. That is crucial. That people in Ireland can understand that we are together, we are a family and we want to defend together the interests of Ireland."
He also said Brexit will be a "hard burden for Great Britain".
"That is the reality and they will face this, and that is nothing to do with punishment," he said.