It says between 2001 and 2013, 4.3 million deaths were averted, 3.9 million of which were children under the age of five in sub-Saharan Africa.
Each year, more people are being reached with life-saving malaria interventions, the WHO says.
In 2004, 3% of those at risk had access to mosquito nets, but now 50% do.
There has been a scaling up of diagnostic testing, and more people now are able to receive medicines to treat the parasitic infection, which is spread by the bites of infected mosquitoes.
An increasing number of countries are moving towards malaria elimination.
In 2013, two countries – Azerbaijan and Sri Lanka – reported zero indigenous cases for the first time, and 11 others (Argentina, Armenia, Egypt, Georgia, Iraq, Kyrgyzstan, Morocco, Oman, Paraguay, Turkmenistan and Uzbekistan) succeeded in maintaining zero cases.
In Africa, where 90% of all malaria deaths occur, infections have decreased significantly.
Here, the number of people infected has fallen by a quarter – from 173 million in 2000 to 128 million in 2013. This is despite a 43% increase in the African population living in malaria transmission areas.
WHO director general Dr Margaret Chan said: “These tremendous achievements are the result of improved tools, increased political commitment, the burgeoning of regional initiatives, and a major increase in international and domestic financing.”
But she added: “We must not be complacent. Most malaria-endemic countries are still far from achieving universal coverage with life-saving malaria interventions.”
Emerging drug- and insecticide-resistance continued to pose a major threat, and if left unaddressed could trigger an upsurge in deaths, she warned.
There are also fears that the ongoing Ebola crisis in West Africa may set back the malaria fight.
Globally, an estimated 3.2 billion people are at risk of being infected with malaria and developing the disease.
Although malaria funding totalled $2.7bn (£1.7bn) in 2013 – a threefold increase since 2005 – it is still significantly below the $5.1bn needed to achieve global targets for malaria control and elimination, says WHO.
Based on current trends, 64 countries are on track to meet the Millennium Development Goal target of reversing the incidence of malaria by the end of this year.