The French commission is due to publish its findings on Tuesday, marking the culmination of two and a half years of work, probing allegations of abuse going back to the 1950s.
"We have estimated the number (of paedophiles) as standing at 3,000, out of 115,000 priests and religious officials, going back to the 1950s," commission head Jean-Marc Sauve told the Journal du Dimanche paper.
A spokesperson representing the French Catholic Bishops' Conference declined to comment on Mr Sauve's remarks.
A Vatican spokesperson said it would wait for the full report to be published before deciding on whether to comment.
In June, Pope Francis said the Catholic Church's sexual abuse crisis was a worldwide "catastrophe".
The French Catholic Church posted a prayer on its official Twitter account on Sunday, on behalf of victims, and added it would also hold a prayer on 5 October – the day of the publication of the report.
"Dear Lord – we entrust to you all those who have been victims of violence and sexual attacks in the Church. We pray that we will always be able to count on your support and help during these ordeals," it wrote on its Twitter account.
Steps to wipe out abuse
Since his election in 2013, Pope Francis has taken a series of steps aimed at wiping out sexual abuse of minors by clerics.
In 2019, the pope issued a landmark decree making bishops directly accountable for sexual abuse or covering it up, requiring clerics to report any cases to Church superiors and allowing anyone to complain directly to the Vatican if needed.
This year, he issued the most extensive revision to Catholic Church law in four decades, insisting that bishops take action against clerics who abuse minors and vulnerable adults. Critics have said he has not done enough.
The French Church, which has seen dwindling numbers of faithful in recent years, said in March it would propose financial compensation to those who were victims of abuse.
Last month, the Roman Catholic Archbishop of Cologne decided to take a "spiritual time-out" from his duties after committing grave errors in a crisis over clerical sexual abuse.
A report published last year in Britain said the Catholic Church received more than 900 complaints involving over 3,000 instances of child sex abuse in England and Wales between 1970 and 2015, and that there have been more than 100 reported allegations a year since 2016.
Readers seeking support can contact Lifeline crisis support on 13 11 14, Suicide Call Back Service on 1300 659 467 and Kids Helpline on 1800 55 1800 (for young people aged 5 to 25). More information is available at Beyond Blue.org.au and lifeline.org.au.
Anyone seeking information or support relating to sexual abuse can contact Bravehearts on 1800 272 831 or Blue Knot on 1300 657 380.