Speaking at the count in Bishopbriggs, outside Glasgow, she said: "These are very significant results for the future of our country and I will be making further remarks later today".
On the morning of Boris Johnson's early Christmas the Liberal Democrats handed over the reins to their sleigh and hoped for a happier New Year.
Scottish Lib Dem leader Willie Rennie has met the party's new MPs to rally them before they head to Westminster next week.
Liberal Democrats leader Jo Swinson has lost her seat in the House of Commons, after pushing policies including overturning Brexit without even a second referendum and allowing people to change gender at will.
Ms Callaghan won Dunbartonshire East with 19,672 votes against incumbent Ms Swinson, who received 19,523 votes.
Other candidates proposed included Hanover-born Bath MP Wera Hobhouse and Layla Moran, the returning Oxford West and Abingdon whose vote increased by 9.5% since 2017.
Meanwhile Ms Callaghan told BBC Scotland she was "delighted" to have unseated the Liberal Democrat leader - who at the start of the election campaign had declared she was running to be the next prime minister.
She said: "Giving people the chance to choose to stop Brexit, obviously it hasn't worked".
She has already said she will seek a second referendum on Scottish independence at the earliest opportunity.
"Boris Johnson may have a mandate to take England out of the European Union, he emphatically does not have a mandate to take Scotland out of the European Union".
However, they gained another seat, North East Fife, from the SNP so their total number of MPs north of the border remained at four.
He added that she was "was the only win from the SNP across Scotland from any party".