She was born in Athea, County Limerick, the eldest of eight children. She was educated locally and at the College of Art in Dublin, and went on to work as a teacher at Coláiste Mhuire in Abbeyfeale, County Limerick. Ahern became involved with the Irish Countrywomen's Association (ICA), becoming the organisation's president, and she also served on the board of Bord Fáilte.
Ahern contested the Dáil elections of 1965, 1969 and 1973, but was unsuccessful on all three occasions. However, she retained her Seanad seat, initially as a Taoiseach's nominee, and in 1969 and 1973 she was elected on the Cultural and Educational Panel. After her re-election in 1973, she was nominated by Fianna Fáil senator Brian Lenihan for the post of Leas-Chathaoirleach of the 13th Seanad. The post had traditionally been held by a member of an opposition party, but the incoming National Coalition government of Fine Gael and the Labour Party decided that it wanted a Labour deputy to Fine Gael Cathaoirleach James Dooge. Labour's Evelyn Owens was elected as Leas-Chathaoirleach, but Ahern won the support not just of her Fianna Fáil colleagues but also of Mary Robinson then an independent senator, and later President of Ireland.
Dáil success came with Fianna Fáil's landslide victory at the 1977 general election, when she was elected as a Teachta Dála (TD) for Kerry North. It was also the first time that two Fianna Fáil TDs had been elected in the Kerry North constituency, the other deputy being Tom McEllistrim. Ahern only served one term as in Dáil Éireann, as she lost her seat at the 1981 general election and retired from national politics. After retirement, she joined the Progressive Democrats in 1985.
When she died in Tralee, aged almost 93, she was the oldest surviving former member of the Oireachtas. Her husband Dan, a national school teacher, had died before her. Her cousin, Fianna Fáil Senator Ned O'Sullivan described Ahern as a highly principled woman, and said that "Kit Ahern had more integrity in her little finger than most of us have in our entire bodies".
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- "Correspondence between Ahern and Seán Lemass in relation to her appointment to the Seanad". Department of the Taoiseach: Women in 20th-Century Ireland. National Archives of Ireland.
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- "Seanad Éireann debates, Volume 58: Private Business: Nomination of Senator". 2 December 1964. Archived from the original on 7 June 2011. Retrieved 2 January 2008.
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- "Seanad Éireann debates, Volume 75: Election of Leas-Chathaoirleach". 20 June 1973. Retrieved 2 January 2008.[permanent dead link]
- "Former Women TDs First Elected 1970–97". Centre for Advancement of Women in Politics. Retrieved 2 January 2008.
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- Donal Hickey (28 December 2007). "Tributes paid following the death of former Fianna Fáil minister Kit Ahern". The Irish Examiner. Archived from the original on 21 May 2011. Retrieved 2 January 2008.