Fingal County Councillor Cian O'Callaghan has announced his resignation from the Labour party.
Mr O'Callaghan, who represented the Howth-Malahide ward, is the third elected representative to leave the party in the last week.
He was Mayor of Fingal last year and was first elected in 2009.
Mr O'Callaghan said he does intend to contest next year's local elections in Fingal.
He said he is interested in working with others on the left who are interested in evidence-based politics.
Mr O'Callaghan mentioned individuals such as TDs Maureen O'Sullivan, Brendan Halligan, Thomas Pringle as amongst those he might be interested in working with.
Ireland East MEP Nessa Childers announced on Wednesday that she had left the party.
Ms Childers had left the Labour parliamentary party in April, but had remained a member of the wider party until this week.
She said she will contest next year's European Elections as an Independent. It is not certain which constituency she will run in.
Labour Councillor Jenny McHugh from Trim, Co Meath defected to Fianna Fáil.
Last month, two councillors in Wicklow, Tom Fortune and Barry Nevin, said they were resigning from the party because it had lost touch with the people.
Heart of Labour party 'sound' - Rabbitte
Minister for Communications Pat Rabbitte said the heart of the party was sound and the solidarity of the elected representatives was solid, with predictable exceptions.
Mr Rabbitte said he expected candidates to be attracted who are committed to the policy of the party not just pavilion members.
He said the party was determined to stay the pace and bring Ireland back to economic recovery.
Mr Rabbitte said the going was very rough and the Government had to rescue Ireland from the shambles in which it found it.