Chelsea made the announcement in a statement released on their official website on Wednesday.
Both players contracts was to expire 30 June but they have now agreed to sign short-term agreement to complete the season at Chelsea.
“As a result of the global pandemic and the subsequent delayed conclusion to the campaign, Premier League clubs unanimously agreed to be allowed to enter into short-term contract extensions with players whose deals were due to expire at the end of this month.
“Willian and Pedro were among those affected, and they and the club have now mutually agreed to extend contracts until the finale of the current season. It means they will be available for our remaining Premier League fixtures in 2019/20, as well as any future involvement in the FA Cup and Champions League.”