John McDonnell has told Sky News he would not stay neutral in a second Brexit referendum.
Labour is pledging to negotiate a new Brexit deal if it wins power in the general election on 12 December.
The party would then put that fresh agreement to a second referendum, alongside the option of remaining in the EU.
Mr Corbyn has previously drawn criticism from some quarters for failing to say which side he would back in the campaign.
The Labour leader has defended the position as a sign of “strength and maturity”.
Asked whether he would follow Mr Corbyn’s lead, Mr McDonnell told Sky’s Sophy Ridge on Sunday: “No, I won’t and I don’t think Jeremy’s asking people to do that.
“I’ll wait until I see the details of the deal that we negotiate.
“I’ve said up until now – I was in the negotiations with the Conservatives for six weeks and I couldn’t see a deal even emerging then that could beat remain, but let’s see what we can negotiate.”
Mr McDonnell said party members and shadow cabinet members will be able to campaign on the basis of their judgement.
The shadow chancellor has previously said he would campaign to remain in a second public vote.
He added that Labour would strike a “sensible deal” with Brussels, “put that back to the British people alongside Remain and people will have to make a judgement around that deal as against Remain”.
Opposition parties have hit out at Mr Corbyn’s position.
Chuka Umunna, the Lib Dems’ shadow foreign secretary, said Labour was “betraying Remain voters on the biggest issue facing the country since the Second World War”.
Mr Umunna, a former Labour MP, continued: “Liberal Democrats will be the strong voice that Remainers need, fighting unequivocally to stop Brexit so we can build a brighter future.”
Conservative Matt Hancock said the policy was an “absolute disaster” and “won’t wash” with voters.
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