"Malaria is still the leading cause of morbidity and mortality," Health Minister Khumbo Kachali said at the launch in the southern lakeside district of Mangochi.
"In 2007, we recorded about four million malaria cases in our health facilities and about 7,000 deaths due to malaria."
The insecticide-treated nets have been bought with funding from the Malaria Global Fund and US President George W. Bush's Malaria Initiative.
Kachali, flanked by South African pop star Yvonne Chaka Chaka, said Malawi "expects to see a marked reduction in mortality and morbidity from malaria."
Up to 20 percent of the total number of patients admitted to hospital -- including HIV-AIDS and tuberculosis (TB) sufferers -- die of malaria each year.
Mosquito net coverage in pregnant women and children is currently estimated at 65 percent, from six percent in 2000, Kachali said.
Chaka Chaka, who helped launch the drive as UNICEF goodwill ambassador, said she was shocked with the number of Malawians infected with the disease.
"This is unacceptable... malaria is preventable and we can save lives by ensuring that pregnant mothers and under-five children sleep under treated mosquito nets. These nets cost only 700 Zambia kwacha (US 20 cents) on the market," she said.
Including the new nets, about 6.3 million dollars (4,000 euros) worth of nets have been handed out for free in Malawi since 2003.
Health experts say the government spends about seven million dollars annually to treat around eight million cases.
Some 60 percent of 12 million Malawians live on one dollar a day and the country's per capita gross domestic product is around 210 dollars per year.