Alex Salmond was speaking to a group of supporters and journalists at a book signing in London.
He predicted that Church of Scotland members were more likely to have voted to remain in the UK than Roman Catholics.
Scotland voted no to independence in September 2014 by 55% to 45%.
In Glasgow 32% of people define themselves as Catholic. The city voted yes in the referendum.
Shortly before the vote a study carried out by Stirling University found that Catholics and people of no faith were the most likely to vote yes.
It said support for Independence was higher among those with no religious affiliation and Roman Catholics than members of the Church of Scotland.
Support for a No outcome was particularly high among Anglican members.
Alex Salmond told the group that he expected this poll would be proved right.
Speaking to Premier before the referendum the Parliamentary officer for the Catholic Bishops' Conference of Scotland, John Deighan, said it could be down to a shift in attitudes north of the border.
He said some Catholics previously felt discriminated against in Scotland because of their faith.
He added: "I worked in an engineering environment before and I had people say, "Don't let the guy in the warehouse know you're a Catholic or he won't give you the equipment you need."
"Things like that happened, I think that's not so much the case now.
"The opposition then was between Catholic and Protestant, that has changed radically."
Speaking to Premier's News Hour after the referendum Christian Labour MSP Siobhan McMahon said: "It is quite clear that we lost a considerable amount of the Catholic vote here in Scotland.
"Particularly the Irish community that have settled here.
"We have to really look at ourselves, that's more to do with the Labour party.
"2011 [Holyrood elections] showed the Catholic vote was moving away from us and we have to look at ourselves and how we win that back."