Venezuela's electoral council has set a presidential election for April 14 to choose the successor to Hugo Chavez.
Acting president Nicolas Maduro will run as the ruling party candidate. Henrique Capriles is expected to run again for the opposition.
Mr Capriles lost to Mr Chavez in an October election. Mr Chavez later anointed Mr Maduro as his chosen successor before undergoing surgery in December for the cancer that led to his death on Tuesday.
Earlier, Mr Maduro was sworn in as Venezuela's acting president, despite the objections of the opposition who said the move violated the country's constitution.
The country's 1999 constitution says the National Assembly speaker becomes interim president in the event of a president-elect's death or inability to be sworn in. The constitution also says a presidential election should be called within 30 days.
Stray fireworks exploded above the capital of Caracas as soon as Mr Maduro was sworn in as president.
Both Mr Maduro and National Assembly President Diosdado Cabello pledged to follow Mr Chavez's example and push his socialist-inspired agenda. "I swear by the most absolute loyalty to comrade Hugo Chavez that we will fulfil and see that it's fulfilled the constitution ... with the iron fist of a people ready to be free," Mr Maduro said.
After Mr Cabello swore in Mr Maduro, the National Assembly president said: "Venezuela will follow the route to socialism."
Opposition leader Mr Capriles said Mr Maduro used Mr Chavez's funeral earlier in the day to campaign for the presidency, in violation of the constitution.
The funeral ceremony drew world leaders, athletes and left-wing celebrities, while multitudes of Chavez supporters watched on giant screens outside.