Former junior minister Ivor Callely is granted bail while the High Court reviews his remission status.
Callely had applied to the High Court after his request for remission of his sentence was turned down by the Minister for Justice, Frances Fitzgerald.
The Minister said she based her decision on the view that a breach of trust and abuse of public funds by a member of the Oireachtas must be considered in the most serious terms.
Callely's lawyers claimed he was being punished for being a politician, and that he was being treated unfairly because his early release would attract "unpalatable" media attention.
56-year-old Callely of Clontarf, Dublin, was jailed for five months in July over fraudulent mobile phone expense claims during his time as a Senator, when he claimed €4,207 in expenses using invoices from defunct companies.
The judge in that case ruled that his position at the time was an aggravating factor, and imposed a custodial sentence.
He is expected to be released from Wheatfield prison some time today, after serving three and a half months.
His bail extends while he is challenging the prison authorities and Minister's decision. If he loses the case, he will have to return to prison to serve the remainder of his sentence.