Carol Nolan has quit Sinn Féin after she opposed its policy on abortion, saying she no longer has a place in a party that she claims does not respect the pro-life views of members.
The Offaly TD had been suspended for three months after she voted against the holding of the abortion referendum.
Last night, Ms Nolan announced her resignation from the party but said she would stay on in the Dáil as an Independent TD.
Sinn Féin supported repealing the Eighth Amendment. Last weekend's ard fheis voted to amend party policy so that its TDs can support legislation allowing for abortion up to 12 weeks.
A second motion calling for Sinn Féin TDs to have a free vote on abortion like Fine Gael and Fianna Fáil was heavily rejected.
Ms Nolan explained her decision to quit, saying: "I feel that as a pro-life republican woman that I no longer have a place in this party, which doesn't recognise or show genuine respect for the pro-life views of members.
"It was disappointing that at the ard fheis ... the party's delegates voted against the motion to allow members to have a conscience vote on the issue of abortion."
Ms Nolan said it was "unethical" to force TDs who were strongly opposed to abortion to vote against their conscience. She said TDs were responsible for the laws they enacted and "if a TD votes for abortion they are responsible for all abortions that happen in this State".
She said: "I cannot and will not support abortion and for that reason I have made a decision to leave Sinn Fein."
Ms Nolan told the Irish Independent she hasn't decided whether she would contest the next election as an Independent. Her resignation brings the number of Sinn Féin TDs down to 22.
Sinn Féin leader Mary Lou McDonald said she regretted Ms Nolan's resignation, saying it was "disappointing but not surprising". "Sinn Féin made every effort to give its members space and latitude to articulate a position contrary to the party's position in the recent referendum campaign on Repeal of the Eighth Amendment. The people have spoken on this issue. The Sinn Féin ard fheis has democratically agreed the party's position to support the forthcoming legislation."