Born in Dublin, Ridge was educated at Goldenbridge College, Dublin and at St Patrick's College, Maynooth, where she graduated with an MA. She worked as a Montessori teacher and then as an external tutor at Maynooth Adult Education Department and at Stewarts Hospital in Palmerstown.
She has been a councillor on the South Dublin County Council since the county's establishment in 1993, and was chair of the Council from 1996 to 1997. She previously represented the same Clondalkin area on the former Dublin County Council, to which she was elected in 1985 and which she chaired from 1992 to 1993.
Ridge stood three times as a Fine Gael candidate for Dáil Éireann, but was unsuccessful on each occasion: in Dublin South-West at the 1987 general election, in Dublin West at the 1992 general election and in Dublin Mid-West at the 2002 general election.
The lobbyist Frank Dunlop, whose allegations of corruption in the rezoning of land in County Dublin were based on his own involvement in much of the alleged wrongdoing, claimed in 2000 that he had paid 16 councillors involved in rezoning decisions including that on the Quarryvale site in west Dublin. Fine Gael's then leader John Bruton established an internal inquiry into the allegations, which reported in May 2000 that that it was while Ridge had received donations from developers (including two payments of £500 each from Dunlop), it was "satisfied that Ms. Ridge did not allow the payments which she received to influence her decision to vote on any of these three motions".
In November 2007, Dunlop told the tribunal had persuaded councillors to arrange the seating at a county council meeting to ensure that Fine Gael councillor Peter Brady could be prompted by Ridge to vote in favour of a motion on Quarryvale. Dunlop told the tribunal that he was in the public gallery at the time of the vote and heard Ridge say to her colleague "for, Peter, for" when the time came for him to cast his vote.
On 10 May 2012, Ridge lost the Fine Gael party whip as a result of the complete findings of the Mahon Tribunal which found that she acted "entirely improperly" by accepting a donation of £1,000 cash from Frank Dunlop during the 1992 general election. On 6 July 2012, she resigned from the Fine Gael party. She said that she was not appealing against the ruling of the party disciplinary committee and was leaving because she could not get fair procedures.
- "Ms. Therese Ridge". Oireachtas Members Database. Retrieved 15 February 2008.
- "Clondalkin councillor Therese Ridge resigns from Fine Gael". RTÉ News. 6 July 2012.
- "Senator Therese Ridge MCC". Fine Gael website. 2001. Archived from the original on 24 April 2002. Retrieved 15 February 2008.
- "Therese Ridge". ElectionsIreland.org. Retrieved 15 February 2008.
- "Inquiry into payments made to Fine Gael representatives: Final report submitted to John Bruton TD leader, Fine Gael". The Irish Times. 12 May 2000. Retrieved 16 February 2008.
- Lorna Reid (1 November 2007). "Voters told where to sit 'in case one needed a dig'". Irish Independent. Retrieved 16 February 2008.