The Australian race, usually the season-opener, was delayed from March to November, but no new date was set for the Chinese Grand Prix, normally held in April.
The record, 23-race season will now begin in Bahrain on March 28, a week later than the originally scheduled start in Melbourne.
"The global pandemic has not yet allowed life to return to normal, but we showed in 2020 that we can race safely as the first international sport to return," F1 president Stefano Domenicali said in a statement.
He added that talks were still underway about the Chinese Grand Prix. An F1 statement said the Shanghai race would be held "later in the season if possible", citing travel restrictions.
"Obviously, the virus situation remains fluid, but we have the experience from last season with all our partners and promoters to adapt accordingly and safely in 2021," Domenicali said.
GMM reports: F1 adding Imola to 'plan B' 2021 calendar
Imola is set to announce that it will once again return to Formula 1's covid-affected calendar.
When scheduled grands prix were cancelled or postponed in 2020, circuits including Imola, Portimao, Mugello and Istanbul were called up to fill the gaps.
Now, with Melbourne and Shanghai set to be postponed in 2021, Monaco likely to follow suit and the scheduled 25 April race date still vacant, it emerges that Formula 1 is once again putting together a 'plan B' calendar.
Italian republications including La Repubblica, La Gazzetta dello Sport and Ansa news agency all claim that Imola's participation on the new 2021 calendar will be confirmed on Tuesday morning.
The Italian circuit is tipped to host its 2021 race on 18 April, with the news to be announced by the president of the Emilia-Romagna region, Stefano Bonaccini, at 9.15am.
In other 2021 race news, Spanish GP venue Barcelona has confirmed that it has inked a race deal with Liberty Media for 2021. The Circuit de Catalunya is already provisionally scheduled to host the race on 9 May.
"We will continue to work to make the Montmelo track a permanent venue (in F1), because Formula 1 for us is not an expense, but an investment," said Catalunya's business minister Ramon Tremosa.