"Go around temptations of radical nationalism and populism, as you have done so far," Tusk, who is Polish, said in a speech delivered in Ukrainian that some of the country's media hailed as "historic".
Ukrainians are due to elect a president on March 31, five years after a popular uprising ousted a Kremlin-backed regime and war erupted between Kiev and pro-Moscow rebels in the east of the country.
European Council President Donald Tusk speaks to Ukrainian lawmakers. Source: NurPhoto
Some 13,000 people have since been killed in the conflict.
Tusk also warned parliament against "internal conflicts", which he said only benefit Moscow.
"Your history, like my own country's history, shows that internal conflicts within our two countries is the greatest gift we can give to that third country", Tusk said, hinting at Russia.
He slammed some EU states for being too critical of Ukraine's efforts to reform and democratise.
"There can be no just Europe without an independent Ukraine. That there can be no safe Europe without a safe Ukraine. To put it simply: there can be no Europe without Ukraine!", he said to a long standing ovation.
Tusk is on a three-day visit to Ukraine which is commemorating the fifth anniversary of the pro-EU Maidan revolution.
President Petro Poroshenko launched an uphill battle for re-election last month. His years in power have seen Kiev seek closer ties with the West as war rumbles on in eastern Ukraine, but critics accuse him of not doing enough to tackle corruption.
President Petro Poroshenko officially announces the start of his election campaign. Source: NurPhoto
Volodymyr Zelensky, a comedian who plays the Ukrainian president in a TV series, is currently favourite to take on the real-life role, according to polls.
Zelensky is also ahead of former prime minister Yulia Tymoshenko, as many voters turn their backs on the political class.
