The Liberal Democrats would legalise selling and growing cannabis if elected, the party has confirmed ahead of publishing its manifesto.
The party would allow licensed shops to sell the drug to over-18s, let people grow cannabis at home and introduce small "cannabis social clubs".
The Lib Dem spring conference in 2016 backed a regulated cannabis market.
The party's manifesto will also include a promise to extend paid parental leave for fathers from two weeks to a month.
Under UK legislation, anyone found possessing cannabis can be sentenced to a maximum of five years in prison, an unlimited fine or both punishments - but many argue that the law is not enforced.
Supplying or producing cannabis, which is a class "B" drug, attracts a maximum 14-year prison sentence, unlimited fine or both, under the Misuse of Drugs Act 1971.
It is legal to consume small amounts of marijuana in some other countries - including Norway, the Netherlands and Portugal - while in other countries police do not arrest people for possession.
In 2001, Portugal became the first country in the world to decriminalise the use of all drugs.
Last year, the Lib Dems backed proposals for a "regulated market" to control the pricing, potency and packaging of sales to over-18s.
The proposals were outlined in a report, co-authored by the government's former chief drugs adviser Sir David Nutt, which argued that cannabis should be taxed - and that doing so could yield up to £1bn a year for the government.
The Lib Dems' Julian Huppert confirmed the policy would appear in its upcoming manifesto to BuzzFeed, saying: "The market is run by criminal gangs and they have no interest in public health - the system is causing huge amounts of harm."
During the 2015 election campaign, the Lib Dems called for drug use to be treated as a health rather than a public policy issue.
Labour in its 2015 manifesto called for better drug treatment services, while the Conservatives said they would introduce random drug-testing in jails.
Speaking last year, the Lib Dems' health spokesman, Norman Lamb, said that "the war on drugs has been a catastrophic failure".
"We criminalise thousands of people, blighting their careers," he said. "When people buy cannabis from criminals, they have no idea what they are buying."
'Health and happiness'
The party is also promising extra paid paternity leave - which it is calling "Daddy Month" in a bid to encourage more sharing of parental responsibilities.
Jo Swinson, equalities minister in the coalition government when shared parental leave was introduced in 2015, said: "More needs to be done to encourage men to take leave when they become a dad.
"Research shows that fathers being more involved in their children's lives is good for children's development and good for the health and happiness of the whole family."
Labour has also said it supports extending paid paternity leave.