MEPs adopted a nonbinding resolution strongly condemning the life sentence an Istanbul court last week handed to Kavala on controversial charges of trying to topple the government.
The 64-year-old philanthropist had already been held without conviction for more than four years.
“The current Turkish Government has deliberately destroyed any hopes of reopening its EU accession process or opening new chapters and closing open ones under the current circumstances,” the resolution said.
It called Kavala’s detention “unjust, unlawful and illegitimate” and demanded his immediate liberation.
The EU’s foreign policy chief, Josep Borrell, said just after the verdict that the bloc’s members “deeply regret” it.
On Wednesday, the EU’s commissioner for international partnerships, Jutta Urpilainen, told the European Parliament that the sentence was “a chilling warning about the shrinking space for civil society in Turkey.”
Kavala, a soft-spoken intellectual and businessman, has denied the charges levelled against him and said ahead of the court’s verdict that he was the target of “judicial assassination.”
He has been accused in the court of funding large-scale anti-government protests in 2013 when Erdogan was prime minister. Erdogan has portrayed him as a leftist agent of the Hungarian-born US billionaire George Soros.
Previously, Kavala was also charged with involvement in a failed 2016 putsch seen as driving a more authoritarian streak by Erdogan.
Turkey’s bid to restart EU membership negotiations has stalled as sharp tensions between Brussels and Ankara flare on numerous issues, including increased repression under Erdogan in recent years.