Mr Rennie’s “penny for education” policy is expected to be at the centre of the proposals, which will also include promises of a “step-change” in mental health services and protection of the environment and civil liberties.
The Lib Dems want to use Holyrood’s new powers to increase income tax rates by a penny in order to raise £475 million each year for education.
The party returned just five MSPs to the Scottish Parliament in 2011 and it hopes to begin its electoral recovery in Scotland on May 5.
Speaking ahead of the manifesto launch in Edinburgh, Mr Rennie said: “Our programme for Scotland is ambitious and progressive. We are offering the biggest investment in education since devolution, new plans for mental health services, new laws to guarantee our civil liberties and new investment so we can exceed our climate change targets.
“To embed these proposals in government policy over the next five years we need more Liberal Democrat MSPs in Parliament. And thanks to the combination of our bold and optimistic proposals and our record of action in Holyrood over the last five years, the party is set to grow again at this election.
“Voters can count on Liberal Democrats to devote the next five years to making Scotland the best again.”
Labour leader Kezia Dugdale will also be in the capital, outlining her plans to prevent cuts to children’s services. Her party also proposes tax rises to fund education.
She said: “I want every single young person to get the best possible start in life. That means a world-class education in the classroom but it also means children getting the opportunity to try something new.
“After-school clubs and extracurricular activities are where young people find out who they are and what they’re good at. Cutting education will cut the opportunities our children enjoy.”
She added: “ Labour will reverse the tax cut for the top 1% so we can stop the cuts and invest in schools. The SNP won’t tax the top 1% and it’ll be our children who lose out.”
Elsewhere, First Minister Nicola Sturgeon and Scottish Conservative leader Ruth Davidson will both target rural voters.
On a campaign visit to Grantown-on-Spey in the Highlands, SNP leader Ms Sturgeon will set out her plans for land reform and support for rural Scotland.
“In the last parliament we took the latest step on Scotland’s land reform journey, with the passage of new and radical legislation,” she said.
“We will set out plans to further empower communities and democratise land ownership in our manifesto, as part of a strong offer of support for rural Scotland.”
Ms Davidson will also travel north to discuss Common Agricultural Policy payments with voters in Aberdeenshire.
The Scottish Greens will highlight their support for community right-to-buy, with party co-convener Patrick Harvie joining campaigners near Stirling who are battling proposals for a development.