Fianna Fáil's Jim O'Callaghan says it would be a breach of his profession's code of conduct if he refused to represent someone legally because of their politics.
It comes after the Irish Independent reported that Mr O'Callaghan was hired by former Sinn Féin leader Gerry Adams to act in a defamation case.
Mr O'Callaghan - who is a long-serving barrister alongside his political career - has been heavily critical of Sinn Féin during the election campaign.
However, the Fianna Fáil candidate for Dublin Bay-South said he separates his private profession and his politics.
Speaking on the Pat Kenny Show, he explained: "I had a significant legal career as a barrister prior to becoming a TD.
"I represented thousands of people... I've represented Fine Gael TDs and ministers, Fianna Fáil TDs and ministers, Labour politicians, people from the SDLP and Sinn Féin, unionist parties in Northern Ireland, prominent businessmen and prominent trade unionists.
"I do not discriminate as a barrister between people who come to me looking to be represented.
"Nor could I, because I'd be breaching the code of conduct of the Bar of Ireland if I decided 'I'm not going to represent that person, I don't like their politics'".
He also stressed that he is not allowed to talk about individual cases.
In a statement, the Bar Council said: "It is the duty of barristers to be independent and free from any influence, especially such as may arise from their personal interests or external pressure, in the discharge of their professional duties as barristers.
"Barristers cannot discriminate in favour of or against any person availing, or seeking to avail, of the services of the barrister on the grounds of race, colour, sex, sexual orientation, language, politics, religion, nationality, national or social origin, national minority, birth or other status.
"This is detailed in the code of conduct of The Bar of Ireland, to which all members of the independent referral bar are bound.
"It is in accordance with the provision that everyone is entitled to access to justice, which is central to trust in the Irish legal system and the rule of law."