Suing a barrister for professional negligence is fraught with difficulty. There was a rule in UK and Irish law that, on the one hand, barristers can't sue a client for unpaid fees, and on the other hand, clients can't sue a barrister for negligence or poor performance. This is based on a fiction that barristers are learned but amateur exponents of oratory and legal knowledge. Their assistance is provided as a courtesy to grateful litigants who reward them with a gratuity or gift. The barrister would never lower himself to the grubby commercial practice of asking for a fee and the client's solicitor would discreetly slip the fee into a pocket in the barrister's gown rather than embarrass him by paying him openly as one might pay a tradesman!
It was only in the last decade that the UK courts changed this rule and barristers can now be sued in UK courts. As far as I know, the Irish courts have not formally set aside the old rule, but the general expectation is that they will if a suitable case arises.
But if you really want to sue a barrister, consult a solicitor and get some good advice first. As a general rule, Irish lawyers don't like suing other Irish lawyers! Might also be worthwhile talking to the Legal Services Regulatory Authority who regulate barristers.