He told CNN he believed there would be a "significant reduction" in Covid-19 cases if every American wore a face covering.
Mr Biden also said he would order masks to be worn in all US government buildings.
The US has recorded 14.1 million cases and 276,000 deaths from Covid-19.
What did Biden say about masks?
In the interview with CNN's Jake Tapper, Mr Biden said: "The first day I'm inaugurated to say I'm going to ask the public for 100 days to mask. Just 100 days to mask, not forever. One hundred days.
"And I think we'll see a significant reduction if we occur that, if that occurs with vaccinations and masking to drive down the numbers considerably."