The election timing is in line with the Himalayan nation's first republican constitution, drawn up in 2015, that requires a new parliament to be in place before January 21 next year.
Law Minister Yagya Bahadur Thapa, confirming the cabinet's decision on the election date, said Nepalis would celebrate their democratic rights.
"This is going to be a big festival. There is no doubt about that," he told Reuters.
Elections to seven state assemblies, set up under the new constitution to establish more of a federal system, would be held at the same time, he said.
The parliamentary election will mark a personal triumph for Prime Minister Sher Bahadur Deuba, who was fired by Nepal's last monarch, King Gyanendra, in 2002.
The king had called Deuba "incompetent" for failing to contain a Maoist insurgency and hold elections.
One of Asia's poorest countries, with nearly a quarter of its 28 million people living on less than $2 a day, Nepal has seen nine different governments since then.
The instability has stifled growth and unnerved investors while two devastating earthquakes in 2015 were a further blow to efforts to stabilise the economy in a landlocked country with the potential to generate significant hydroelectric power.
Heavy monsoon rain in recent days has brought floods to Nepal's low lands and killed more than 130 people.
Political developments in Nepal are closely watched by neighbours India and China.
Nepal is also in the middle of phased local elections - the first in two decades - with a final round set for September 18.