The South Lakes MP has called for the legalisation of cannabis for recreational use.
Tim Farron, who's also leader of the Liberal Democrats, will back a motion calling for his party to extend its existing support for the legalisation of cannabis for medicinal use to recreational use.
The motion follows the release of findings from an expert, Lib-Dem appointed panel.
Mr Farron becomes the first main party leader to propose decriminalising the drug for social use.
He said: “I believe in evidence-based policy making and making sure that decisions are made with all the information available and in the public domain.
“I think this furthers public policy making and delivers better outcomes.
“The party went into the last election proposing that drug use should be treated as a health issue and allowing police to focus on those manufacturing, importing or dealing in illegal drugs.
“With that in mind, the Liberal Democrats will be releasing a report of independent experts in the coming weeks talking about the issue.”