Former Catalan Vice President Oriol Junqueras has committed to obey the law, speaking to a panel of judges that are reviewing an appeal against his provisional jailing.
Mr Junqueras faces potential rebellion and other charges for pushing ahead with an illegal independence bid for the wealthy Spanish region.
He is seeking to regain his freedom to become a politician following elections last month.
The public prosecutor says the court should uphold the jailing because of the risk of further crimes being committed.
Mr Junqueras’ lawyer, Andreu Van den Eynde, said the politician vowed to seek negotiations and a bilateral dialogue with Spain on the Catalan issue.
“He asked to be freed, to represent the people who voted for him, to be with his family, and to let him manage this situation which demands political maturity,” the lawyer said.
A decision is expected on Thursday or later.