THE LibDems took the seat in the Corstorphine-Murrayfield by-election on the first round of vote counting.
The win could spell trouble for the ruling minority Labour administration, with the LibDem win taking the party to 13 councillors, to Labour's 12.
Fiona Bennett, the party's candidate, will now serve on Edinburgh City Council, becoming the third LibDem to represent the ward.
Bennet returned 4557 votes and was elected at the first stage. The SNP candidate Donald Rutherford was runner-up with 1086.
Fiona Bennett, Scottish Liberal Democrats, has been elected as a new councillor in the Corstorphine/Murrayfield ward by-election, with a turnout of 42.3% pic.twitter.com/9MnBXixZjk
— The City of Edinburgh Council (@Edinburgh_CC) March 10, 2023
The remaining seven candidates gained less than 1000 votes each.
The SNP's 18 councillors make them the biggest group in the local authority, but the LibDem win demotes Labour to the third largest party.
Last night, ECC tweeted: "Fiona Bennett, Scottish Liberal Democrats, has been elected as a new councillor in the Corstorphine/Murrayfield ward by-election, with a turnout of 42.3%."
Scottish LibDem leader Alex Cole-Hamilton dubbed the win an "extraordinary victory".
He added: “I am delighted to see Fiona Bennett storm to victory. Improving the lives of her community and the people around her is what Fiona is all about and she will now do that to great effect from the city chambers of our nation’s capital.
“Fiona ran a campaign forged in the finest traditions of our party and by so doing, she and her team delivered the biggest local authority by-election victory in our history.
“There is now a corner of West Edinburgh made solid gold by her success. It is represented at every level of democracy by our party and our party alone.
“By electing Scottish Liberal Democrat councillors, we can improve communities and change lives. It’s in our DNA. And the engine rooms that we are establishing around the country will help to lift our vote at every parliamentary election as well.”
Cole-Hamilton celebrated the by-election win
Newly elected councillor Fiona Bennett said: “I would like to thank everyone who voted for me and everyone who came out to campaign on my behalf.
“I am delighted to have won this election and now I will be getting to work to represent the people of Corstorphine/Murrayfield.
“Whether it’s fixing our broken roads and pavements, action on air pollution, measures to tackle flooding, or supporting local traders, there’s so much to do.”
The Corstorphine-Murrayfield now has three LibDem councillors, with Bennett joining colleagues Alan Beal and Euan Davidson on the local authority.
Until last month, Labour had 13 councillors in the administration and ran the city with Tory and LibDem support.
On February 23, Sighthill-Gorgie Labour councillor Ross McKenzie quit the party in the middle of a full council meeting, reducing the party to 12 representatives.
Full list of results, round one.
Scottish Liberal Democrats 4577 (56%)
SNP 1086 (13.3%)
Conservative 788 (9.7%)
Labour 568 (7%)
Green 417 (5.1%)
Independent Elaine Miller 327 (4%)
Independent Pete Gregson 295 (3.6%)