House Speaker Nancy Pelosi warned anyone who breaks the new rule face being removed from the chamber.
She took the decision after Louie Gohmert, a Texas Republican often seen around the Capitol without a face covering, tested positive on Wednesday.
He had been due to travel that day with US President Donald Trump.
Mrs Pelosi, a California Democrat, said on the House floor on Wednesday evening that members would be allowed to remove their masks when addressing the chamber.
"The chair expects all members and staff to adhere to this requirement as a sign of respect for the health, safety, and wellbeing of others present in the chamber and surrounding areas," she said.
Mrs Pelosi said she would view "failure to wear a mask as a serious breach of decorum", warning the House Sergeant at Arms could kick out anyone who did not wear a mask.
According to GovTrack.us, 10 members of Congress - three Democrats and seven Republicans - have confirmed they tested positive, or were diagnosed with coronavirus.
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