He defeated rival Layla Moran by 42,756 votes to 24,564 to take over from Jo Swinson.
Willie Rennie says he is trying to entice the party's former UK leader to run in next year's Scottish Parliament election.
The party said it made the move because the country was in its biggest crisis since the Second World War.
Inquiry accuses former Liberal leader of 'abdication of responsibility' over child sex allegations against late MP Cyril Smith.
Data released to the Scottish Liberal Democrats under freedom of information legislation has been branded 'miserable'.
Tim Farron says anyone can win a title if 'the opposition is abysmal'.
She only became leader of her party in July but has been unseated by the SNP's Amy Callaghan.
All the main UK-wide parties have now revealed their pitches to voters ahead of December 12.
The Scottish Lib Dem leader told STV's Scotland Tonight that his party wants to stop both.
An Ipsos MORI survey found 44% of voters will pick Nicola Sturgeon's party on December 12.
The Liberal Democrat leader has succeeded in a bid to stop the SNP from distributing a leaflet.
The party is pledging 'no to indyref2' as its pitch to voters ahead of the December 12 poll.