The parliamentary election will coincide with local votes in 65 municipalities, including the capital Belgrade.
Experts say the vote and an absence of a working parliament, will allow Vucic to buy time and delay decisions over ties with independent and predominantly Albanian Kosovo, which Serbia still sees as its southern province.
Opposition parties and rights groups accuse Vucic, the SNS and its allies of autocracy, oppressing media freedoms, election fraud, violence against political opponents, corruption and ties with organised crime.
After signing the decree, Vucic said it was important for Serbia to "preserve peace, stability, and internal cohesion and (to) show democracy".
"This campaign is an opportunity to present different ideas, programs, policies ... , but which must never threaten vital interests of Serbia," he said.
Persons:
Aleksandar Vucic, Vucic, Ursula von der Leyen, Stata, Aleksandar Vasovic, Andrew Cawthorne, Alison Williams
Organizations:
EU, Russia, Serbian Progressive Party, SNS, Thomson
Locations:
BELGRADE, Serbian, Kosovo, Belgrade, Albanian Kosovo, Serbia, Ukraine