The Scottish Liberal Democrat leader insisted he would team up with “people from all parties” to try to protect Britain’s relationship with the European Union.
His comments come after the Scottish Labour conference highlighted divisions in the party over Europe, with prominent figures including former leader Kezia Dugdale, MP Ian Murray and MEP Catherine Stihler all speaking out in favour of the UK staying part of the single market.
A new campaign group, Scottish Labour for the Single Market, has also been set up within the party.
Mr Rennie, praised the “tenacity and determination” of this group in opposing the stance the party has adopted under Jeremy Corbyn.
Speaking ahead of the speech to the Fife for Europe group, Mr Rennie said: “The Liberal Democrats will work with people from all parties who want to protect our relationship with the European Union.
“I was particularly impressed by the tenacity and determination of Labour members who are signed up to the Labour for the Single Market Campaign.
“They stood up against the leadership of their party who are determined to deliver Brexit alongside Theresa May’s Government.”
He added: “Brexit is one of the biggest decisions for a generation and it is a decision that will damage our economy, jobs and standard of living.
“That is why it is important that pro-Europeans in every party stand up for the best interests of our country.
“Increasing numbers of people, including members of Labour for the Single Market, back the British people having the final say on the Brexit deal.
“Momentum is building and it is therefore important we work together across parties to save us from a damaging Brexit.”
Scottish Labour for the Single Market co-chair Ian Murray MP said: “The campaign to protect jobs and workers’ rights is much bigger than the Labour Party. We need to unite the country, and to achieve that we need cross-party co-operation.
“Theresa May does not command a majority in the Commons for a hard Brexit. With political will, the UK can remain in the Single Market and ensure that tens of thousands of jobs are not lost as a result of Brexit.
“Yet the ball is in Labour’s court. It is my party which, if it chooses, can ensure we take the least-worst Brexit option if we are to leave the EU.
“We owe it to future generations to remain in the single market and customs union.”