Mr Rennie will invoke the memory of Charles Kennedy in a speech to party activists and supporters in Paisley, arguing the referendum debate was “at the heart of his ideals, his compassion and his hard-headed sense”.
He will say the former Liberal Democrat leader who died suddenly last June at the age of 55 would not have wanted to miss out on the campaign for Europe.
With just days to go before the poll, Mr Rennie is expected to say: “I look at his words in his speech to the Council of Europe in June 2014, two years ago. He quoted Robert Burns and the need to see ourselves as others see us. And in the next five days, that is surely the poetry everyone in Scotland and the whole UK needs to think about.
“What message would we send around the world if we said that we can’t work with others, that we can’t co-operate, that we always know best? Why would people take us seriously in the capital cities and the company boardrooms in Madrid, Delhi or Washington DC?
“If we declare that we will not co-operate with our neighbours, why would others truly believe that we will work with them?”
Mr Rennie will say the voice of his former colleague had been sorely missed in a week that saw both the homophobic terror attack in Orlando and the fatal shooting and stabbing of Labour MP Jo Cox.
He is expected to say: “It has been a dark week for freedoms and democracy. Forty-nine people murdered in a gay club in Orlando a week ago shocked us all. The murder of Jo Cox in the line of her duty left us numb at the senselessness of it all.
“This is a week when I needed to hear the compassion, the common sense and the decency of Charles Kennedy. He could speak about the idealism. He could speak about the dreams. And he could speak too, of the hard-headed economics of remaining in the European Union.
“The European Union is a story of a 50-year mission, through the European Union, to ensure that Europe is never again ravaged by poverty, unemployment and war.
“We in this country are, as Charles Kennedy was, a force for good in the world, however imperfect. We should work with that grain, rather than give up in despair. Our work for good in the world is amplified and extended within a European Union.”