While the leaders of key eurozone countries expressed relief at the proposed deal, parties from Britain's right-wing UKIP to Spain's radical left Podemos said Greece had been stitched up.
The deal even sparked a trending Twitter hashtag, #ThisIsACoup, which became one of the most used terms online on the social network in Greece, France, Germany and Britain.
Critics abroad saw Greece as a victim of financial bullying - notably in Spain, which has been rattled over recent years by fears of contagion of eurozone financial instability and holds a general election this year.
"What they are trying to do in Greece is launch a financial coup d'etat and convert it into a protectorate," said Pablo Echenique, a regional deputy from Podemos. "There is no European solidarity."
German Chancellor Angela Merkel led eurozone leaders in persuading Greek Prime Minister Alexis Tsipras to push through tough cash-saving reforms in return for a third rescue package worth between €82 and €86 billion ($95 billion).
Under the deal, Tsipras has to introduce tough conditions on labour reform and pensions, VAT and taxes and privatisation measures by Wednesday.
Negotiations 'at gunpoint'
In France, an opposition group allied to Podemos and Syriza, the Party of the Left, joined in condemnation of the way Greece was treated in negotiations led by Merkel and French President Francois Hollande.
"That's how the European Union is. A revolver to the head, a nation choked and placed under a financial blockade, which has to make a so-called agreement after 17 hours of talks," said the party's co-founder Jean-Luc Melenchon.
A failure to reach a deal would have likely led to a collapse of Greek banks within days unless the country de facto exited the eurozone by introducing a new currency.
The financial terms of the deal are much the same that was on offer, but now include Greece being forced to put state assets into a privatisation fund that is expected to generate €50 billion in revenue.
And Athens will be on a short leash, with the government needing to get the approval of the European Commission, European Central Bank and International Monetary Fund before making public draft legislation or submitting it to lawmakers.
Italy's prominent anti-euro Five Star protest party leader Beppe Grillo accused eurozone leaders of using a "strategy of terror".
"The humiliation of Greece is a warning to all countries who want their sovereignty to be recognised," he said.
Criticism flared in another southern European country sensitive to eurozone jitters: Portugal, which in 2011 was bailed out by international creditors as Greece had been a year earlier.
"This is not an agreement, it has been imposed," said Catarina Martins, leader of the Portuguese anti-capitalist party Left Bloc.
"Democracy has been completely swept aside to make way for the colonial-style impositions."
Nobel-winning economist Paul Krugman quoted the Twitter hashtag #ThisIsACoup in a blog in the New York Times.
"This goes beyond harsh into pure vindictiveness, complete destruction of national sovereignty, and no hope of relief," he wrote.
"It's a grotesque betrayal of everything the European project was supposed to stand for."
Eurosceptic parties in several countries also decried the way Greece had been treated.
"If I were a Greek politician I would vote against this deal. If I were a Greek 'no' voter I would be protesting in the streets," said Nigel Farage, leader of Britain's anti-EU party UKIP.
"Mr Tsipras's position is now at stake. This conditional deal shows that national democracy and membership of the eurozone are incompatible."
Britain's Prime Minister David Cameron has promised a national referendum by the end of 2017 on whether to leave the European Union.
The leader of Italian right-wing anti-euro Northern League, Matteo Salvini, called the deal a "farce" for handing Greece more money but not reforming the EU treaties.
The French National Front's vice-president Florian Philippot called it "the enslaving of an entire people" to "save the euro at any price".
"If the agreement goes ahead, Greece will emerge washed out, even dead."