Sinn Fein's Angela Donnelly took a seat in Fingal County Council, after her colleague Aaron O Ruairc resigned.
Cllr Donnelly was welcomed into the chamber and praised for her community work over the years.
Ms Donnelly is the wife of TD Paul Donnelly and was only nominee for the vacant seat.
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It was a history day for Sinn Fein as they became the first all-woman council.
The new councillor thanked Fingal County Council for the opportunity and promised that she would represent those marginalised by society.
She wished Aaron O Ruairc well, who had resigned from the council in December due to work commitments.
She said: "I'd also like to thank Aaron O Ruairc for his service on this council which has come to an end.
"However his service to Sinn Fein and his community continues.
"He's a wonderfully talented young republican and we very much hope that he will return to public office in the future when the time is right for him."
She spoke of the difficulties that often come with being a female politician and how more inclusion is needed.
Cllr Donnelly said: "It's amazing to be part of a team on Fingal County Council that has four female councillors.
"To have an all-woman team is very special . To ensure women's equality, we need to see where women are. I've been an activist for over 30 years and like every other woman I know that is active in their community or with young groups, my activism has been in the context of a life raising a family and caring for my mother.
"Does that make my work and my experience to date less than that of work and experience in the public sphere? No, it does not.
"I'm proud of my activism and contribution to society. I am proud of the other women like me.
"Public life can be a very challenging realm for women and our political public sphere needs to change so women can participate equally.
"It needs to be expanded to view women's contributions in all of its forms.
"I'm honoured to be joining the sphere of political representation but it is not more meaningful than my contribution to date. It is just different.
Donnelly stressed that it was important to give the voices that are often silenced an opportunity to speak.
She said: "I will use my role to give back to those who are marginalised or silenced. I will not speak for them. I will get the microphones and platforms and together we will make sure that there are more voices and that we are all heard.
"That's what real feminism is about. Not creating new hierarchies of exclusion but creating new platforms of inclusion."
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