The pro-independence MSP suggested the halfway mark in the UK’s two-year period of negotiations to leave the European Union (EU) was a “reasonable guess” about the timing of another ballot.
Mr Harvie made the comments after First Minister Nicola Sturgeon explicitly ruled out staging a vote on independence in 2017.
The Green politician agreed with the SNP leader that the option of staging another referendum in the future needed to “remain on the table”.
Almost immediately after the European referendum, in which Scotland voted to Remain but the UK as a whole backed Leave, Ms Sturgeon warned another vote on Scottish independence was “highly likely”.
UK Prime Minister Theresa May has already set a March deadline for triggering the Article 50 process and starting the formal negotiation period.
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Mr Harvie told BBC Radio Scotland: “I don’t think anyone expected a second referendum to be held this year, what has been very clear is that the option needs to remain on the table, and we support that.
“That means the legislation to allow Holyrood to make that decision has to be progressed this year.”
He added that the “lack of clarity” from the UK Government over its negotiating strategy meant it is “very hard to see through the mists of Brexit” at the moment.
He told the Good Morning Scotland programme: “I think a reasonable guess at the moment might be that if Scotland chooses to have this question put again, if the UK chooses to dig its heels in and refuses to respect the way that Scotland voted to remain in the EU, then maybe at some point round about the halfway mark of the two-year Brexit negotiation period, or not long after that halfway mark, we might need to be in a position to put that question to the public.
“There is a contradiction between the 55% vote in 2014 to stay in the UK and the 62% vote last year to stay in the European Union.
“I think we need to explore the options to see if both of those votes can be respected, but if the UK Government refuses, if they refuse to budge from their hard Brexit, no special arrangements for Scotland position, then that contradiction will stand, and it may be that only the Scottish people are in a position to resolve that contradiction.”