Former Fianna Fáil TD for Cork East Ned O'Keeffe has been released from garda custody without charge.
A file is to be prepared for the DPP.
Mr O’Keeffe was arrested at his Mitchelstown home on suspicion of using a false invoice to claim for mobile phone expenses while he was a member of the Dáil.
He walked from Cobh Garda Station shortly after 10.30pm accompanied by his son, solicitor Ciaran O'Keeffe, who made a short statement on behalf of his father.
He said "obviously the dramatic events of the day have taken Mr O'Keeffe by surprise. However, during the course of the day he has cooperated fully with the gardaí and assisted them in their inquiries and has nothing further to add at this time."
When asked how the former TD was, he made no reply.
Mr O'Keeffe was driven away from the garda station by his son.
Ned O'Keeffe represented the Cork East constituency for almost 30 years and served as a junior minister in the Department of Agriculture under Bertie Ahern.
He resigned from that position in a controversy relating to his family's pig farm.
He stood down from politics prior to the 2011 General Election.