President Ellen Johnson Sirleaf said that Liberia had “crossed the Rubicon” and would be celebrating a concerted effort to stem the disease.
More than 4,700 deaths from Ebola have been recorded in Liberia, more than in any other affected country.
Neighbouring Guinea and Sierra Leone continue to fight the outbreak.
It has claimed over 11,000 lives across the region since last year.
The WHO regards a country Ebola-free after a 42-day period without a new case – twice the maximum incubation period.
The last confirmed death in Liberia was on 27 March. On Saturday the World Health Organization said in a statement: “The outbreak of Ebola virus disease in Liberia is over.”
President Sirleaf said, “We will celebrate our communities which have taken responsibility and participated in fighting this unknown enemy and finally we’ve crossed the Rubicon. Liberia indeed is a happy nation.”
Officials say Ebola was eventually conquered in Liberia through a collective effort. Care centres and hand-washing stations were set up to try to halt the disease, which spreads through contact with sick people.
Billboards went up with slogans such as “Ebola is real”, “Wash your hands and don’t touch” and “Don’t be the next victim”.
Although Liberia has now been declared Ebola-free, correspondents say the outbreak will have a long-term impact on Liberia’s fragile economy.
The current outbreak is the deadliest in history. It initially centred on Guinea’s remote south-eastern region of Nzerekore in early 2014, and later spread to Liberia and Sierra Leone.
The WHO is warning against complacency. Its statement warns that there is “a high risk that infected people may cross into Liberia over the region’s exceptionally porous borders”.