Tusk was given the green light to continue in the post until 2019 despite fierce opposition from Poland, his home country, which had put forward Polish centre-right MEP Jacek Saryusz-Wolski.
Saryusz-Wolski is a member of the Civic Platform (PO) party in Poland but, much to the anger of the EPP group in Parliament, accepted the nomination of the country's ruling Law and Justice party to run against Tusk.
Tusk was nevertheless reappointed President, with the backing of 27 member states, at the first day of a two-day EU summit in Brussels on Thursday.
"I don't see how one country could oppose this solution when all the others are in favour," French President François Hollande said.
But Poland's government argued that Tusk supports the domestic opposition in Poland and has failed to protect the country's interests in the EU.
And, speaking on Friday, Polish Prime Minister Beata Szydło said that she does not accept the summit's conclusion to reappoint Tusk.
She said, "It's clearly written that summits end with conclusions. If one country doesn't accept it, it means the summit is not relevant. If now there is a way to find a different solution, that only shows that there are no rules. And Poland doesn't agree with this. And I definitely won't accept any document from this summit."
In his acceptance speech, Tusk who has been in post for two and a half years during which time he has faced several crises, including migration and Brexit, admitted that he had been reappointed in "unusual circumstances."
"As you know, solidarity has always been important in my personal and political life and I really know how much it matters. I know also that it may sound like a paradox because of the context, but your decision is an expression of our unity today.
"I will work with all of you without any exception because I am truly devoted to the united Europe. And I promised myself not to let you down. We must simply start our work again."
The decision to keep him in the post was broadly welcomed, including by Joseph Muscat, the Prime Minister of Malta, the current holder of the rotating EU Council presidency.
Muscat said Tusk was "a strong man with strong European convictions."
Tusk is only the second person to hold the position of European council President, which was created in 2009 to boost EU leadership.
He recently mocked the British foreign secretary, Boris Johnson, for expressing a desire to have his Brexit cake and eat it and classed the unpredictable behaviour of US President Donald Trump as one of the biggest threats facing Europe.
Following his re-election, EU leaders are discussing rising tensions in the western Balkans and the state of the EU economy.
The summit reconvened on Friday, without UK Prime Minister Theresa May, as the 27 leaders look to the future of the EU without Britain.