Willie Rennie is to set out the “emotional” case for the Union in his Scottish Lib Dem conference speech.
Mr Rennie will tell delegates in Perth that he will “stand up for our United Kingdom” as an “uplifting, mutually beneficial partnership”.
Delegates will debate policies including the UK and Europe and maternal mental health before Mr Rennie’s speech.
The two-day event has also heard from MPs Nick Clegg and Alistair Carmichael.
Each man hit out at the rise of nationalism, something Mr Rennie will echo in his keynote speech.
Looking ahead to a potential second Scottish independence referendum, Mr Rennie will tell delegates that the Lib Dems would “lead the way on the kind of campaign for the United Kingdom that we want to see”.
‘Positive, uplifting case’
He is expected to say: “We know the economic case for independence is weaker than even in 2014, so I will not dwell on that today.
“The new case for the United Kingdom is a positive, uplifting one that focuses on the ties that bind us rather than the differences some would use to divide us.
“It is that emotional case. It is the Liberal case for unity. The compassionate case. It goes to the heart of who we are.
“Our United Kingdom is an uplifting, mutually beneficial partnership that we should cherish rather than trash.
“So as we head into another referendum the responsibility on liberals is great. We must stand up and be counted for our values. This is a battle of ideas and values, not of identities and flags.”
Members have so far approved policy motions backing moves to cut drug-related deaths including “safe injection facilities” and the “de facto decriminalisation of the possession of drugs for personal use”, and on increasing the speed limit for HGVs.
The party also reaffirmed its backing to the “Frank’s Law” campaign for free dementia care for those aged under 65.