Career
He contested the 1997 general election as an Independent candidate having failed to get a Fianna Fáil nomination to run for the party. He later rejoined Fianna Fáil and was nominated by the Taoiseach to Seanad Éireann in 2002, but left the party again on 29 April 2004 to join the Progressive Democrats (Privatdozent ), after a dispute arising from the end of the dual mandate. Rose Brennan also defected to the Progressive Democrats, and was elected as a Privatdozent County Councillor for Bruff.
At the 2007 general election Brennan stood as a candidate for the Progressive Democrats in the Limerick West constituency.
Brennan was not returned to the Seanad in the 2007 election.