Roscommon Labour Senator John Kelly demanded that his party and Fine Gael uphold their pre-election pledge to establish an independent inquiry into the priest's death.
"When something looks and smells like a rotten apple, it certainly is a rotten apple," he said. "This man was left to die for up to six hours following a wedding in Clara. Fr Molloy's father was a senator in this House. I think we ought to give him justice. Prior to the general election, Fine Gael and Labour pledged to establish a Commission of Inquiry into his brutal murder and this must be honoured."
The senator was joined by several other Government colleagues in his demands for an inquiry.
Fr Niall Molloy (52), a popular Roscommon priest, was battered to death in the mansion of his friends, Richard and Therese Flynn, in Clara, Co Offaly, in July 1985 after seeking the return of a large sum of money owed to him by Mr Flynn.
Shortly before his death, he had just been voted Roscommon man of the year.
A number of Fianna Fail politicians were present in the house on the evening of the murder including a household name.
The Garda investigation that followed involved a catalogue of failures and bizarre inconsistencies.
Explosive
A two-year probe by this newspaper uncovered significant new evidence, which points to a high-level cover-up involving several pillars of the State.
Mr Kelly commended the Irish Independent for its "untiring investigative work" and said any inquiry must be independent.
"We cannot have gardai investigating other gardai," he said.
Clare Fine Gael senator Martin Conway backed Mr Kelly.
He said: "Justice must be done. Why has it not been done? After 18 months in government, why has a commission of investigation not been appointed?"
Senator Fidelma Healy Eames, also FG, called on Justice Minister Alan Shatter to come to the House and address "the serious allegations of a botched inquiry and cover-up".
Independent senator Marie Louise O'Donnell also called for an inquiry and asked Mr Shatter to come before the House.
Labour Senator John Gilroy also supported calls for an inquiry.
Labour Senator John Whelan for Laois Offaly called on Mr Shatter to "fulfil a commitment given to the Molloy family... prior to the General Election".
"The culprits, those responsible for the murder of Fr Niall Molloy, are walking free," he said. "The public will not accept this is the case. Explosive and persuasive new evidence is now available thanks to the incredible investigative journalism conducted by the Irish Independent which needs to be pursued by the authorities. A Commission of Inquiry is the only way for justice to be done and seen to be done."