Mr Blair is likely to be received into the Church within weeks at a private chapel of Cardinal Cormac Murphy-O'Connor, the Archbishop of Westminster.
Just before completing his term, Mr Blair met with Pope Benedict and was believed to have told him of his determination to leave the Church of England. He also met with Pope John Paul (pictured) on several occasions.
UK Catholic publication The Tablet disclosed the impeding conversion may take place at the end of November.
Blair's spokesman did not deny the story, saying it was “speculation”, Daily Mail reported.
Mr Blair’s wife Cherie and their four children are all Catholic and the family have worshipped together in the past.
However, his conversion is likely to divide Catholics because as an MP Mr Blair voted for abortion at up to 24 weeks, a stance that drew a public rebuke from the late Cardinal Thomas Winning.
Tony Blair will become a Catholic 'within weeks' (Daily Mail, 08/11/07)
British PM to become a Catholic, family priest hints (CathNews, 18/5/07)
Westminster Cardinal and Blair in condom clash (CathNews, 4/12/07)
Pope appeals to Blair against Iraq war (CathNews, 24/2/03)
9 Nov 2007