Mr Brown made the prediction in a election leaflet posed on social media which said: “The next independence referendum could be held in 12 months or two years”.
The issue of when indyref2 should be held has dominated the contest between Mr Brown, the SNP group leader on Inverclyde Council Chris McEleny and SNP activist Julie Hepburn.
Cllr McEleny is campaigning on the grounds that a second vote should be held within 18 months in a bid to attract support from hard line independence supporters.
Until now Mr Brown has confined himself to saying that the SNP “had a job to do” to get the party ready for a tilt at a second referendum.
But ahead of hustings this weekend, Mr Brown, who as Economy Secretary serves in Nicola Sturgeon’s Cabinet, the National reported that he had posted a more direct message on social media.
He said: “The next independence referendum could be held in 12 months or two years. As the First Minister has said, the time to make the decision will be later this year when the timing and shape of the Brexit deal and the extent of the damage it will do to Scotland becomes clearer. That is something no-one can predict at this stage.”
He added: “My job if elected as depute leader will be to make sure we are ready to win the referendum whenever it comes, that we use the time between now and then to engage our membership, hone the case for independence and heighten our organisational and campaigning capacity to get us fighting fit to win.”