Fine Gael TD Nicky McFadden has died aged 51.
The party confirmed that the Co Westmeath TD passed away this afternoon at her family home.
Ms McFadden had been diagnosed with motor neurone disease in December 2012.
She was elected to the Dáil for the Longford-Westmeath constituency in the 2011 General Election.
Ms McFadden was the first female Fine Gael TD in Westmeath.
She was first elected to Athlone Town Council in 1999, when she topped the poll.
In 2003 she was co-opted onto Westmeath Co Council, when her father, Brendan McFadden, retired.
She unsuccessfully contested the 2007 general election, but entered the Seanad in September of the same year.
Born in Athlone, Ms McFadden was educated at St Joseph's College Summerhill. She went on to do a diploma in legal studies at the Athlone Institute of Technology.
She worked as a medical secretary, and later with the ESB.
In recent months her sister, Cllr Gabrielle McFadden, who is the current Mayor of Athlone, carried out official functions when Ms McFadden's condition deteriorated.
Other Fine Gael party members and elected representatives in Athlone also helped to support her during this time.
Ms McFadden is survived by her two adult children, Caren and Eoin.
President leads tributes to McFadden
President Michael D Higgins said Ms McFadden made an outstanding contribution as a Senator and deputy.
He said she showed immense courage in continuing her public service after having been diagnosed with a serious illness.
In the Dáil, Taoiseach Enda Kenny said he believed he was speaking for everyone in the House when he said he was devastated by the suffering and the passing of Ms McFadden.
However, he said he was uplifted by her courage.
He said it was appropriate that she had passed away on the feast of the Assumption, as she was now free of the suffering that had marked the last few months of her life.
Mr Kenny said Ms McFadden was a woman of great joy.
He said he had called to see her on Friday last on his return from Brussels.
The Taoiseach extended his sympathies to her family.
Tánaiste Eamon Gilmore said all members of the House had been shocked when they learned of her illness some time ago.
Expressing his sympathies, Fianna Fáil leader Micheál Martin said Ms McFadden had represented the very best of commitment to public service.
Sinn Féin leader Gerry Adams said he was always struck by the way Ms McFadden was very positive about her illness.
Speaking on behalf of the Technical Group, Independent TD Maureen O'Sullivan said Ms McFadden had a positive attitude to the "cruel, cruel illness".
A minute's silence was held in the Dáil chamber for Ms McFadden before business was suspended for 15 minutes.