Kavala, 65, was sentenced to life in prison without parole in April 2022, while seven others in the case received 18 years based on claims they organised and financed nationwide protests in 2013.
Sanchez thanked Turkish ministry of justice and foreign affairs on social messaging platform X.
"I hope this openness is a sign of a new period for the EU-Turkiye relations," he added.
Sanchez called on Turkish authorities to implement the European Court of Human Rights rulings with regard to Kavala and other cases.
The European Commission's annual report criticised Turkey for not implementing a ruling of the Grand Chamber of the European Court of Human Rights that called for the release of Kavala, who was detained in 2017 over attempting to oust the government.
Failure to comply with the Kavala ruling showed it has been "drifting away from the standards of human rights and fundamental freedoms to which it has subscribed as a member of the Council of Europe", the report said.
(Reporting by Burcu Karakas, editing by Edward Tobin)
