At the weekend, Mr Corbyn reiterated that Labour would back Remain in a fresh vote in order to prevent a no-deal Brexit or an unacceptable agreement reached by Boris Johnson.
He declined to say, however, whether the party would back staying in the EU if it won a general election and negotiated it's own deal with the bloc.
But speaking to Sky News Australia, the shadow foreign secretary, who attributed her party's dire performance to the party's unclear Brexit stance earlier this year, said Labour should now unequivocally back Remain, "no ifs, no buts".
"I genuinely believe that the vast majority of people in Britain will want to Remain, which means I think that any deal, or no deal, or whatever this government comes up with, should be put back to the British people so they can be asked, is this what you voted for? Because if you did, that's fine," she said.
The shadow foreign secretary added: "We don't think it is what you voted for and I am firmly of the view that Labour's policy should be that whatever a government comes up with, no ifs, no buts, no buts as Boris Johnson says, we should put it back to the people."
"We should have another referendum, and Labour should campaign to Remain."
She went on to say people she has spoken to "appreciate that", and say if there is an opportunity to remain in the European Union, "we should take it. Because if we don't, we're off our bloody rockers".
Challenged on Labour's Brexit policy on Sunday, Mr Corbyn told Sky News' Sophy Ridge that in the event of a no-deal Brexit, his party would "campaign to Remain".
Pressed on his position if he was prime minister and negotiated a Brexit deal, however, he replied: "Well we have got to get into office first to negotiate a deal, we've got to win an election first and then we'll reopen those talks with the EU but at the moment the danger is a no-deal exit on 31 October with all the problems that that brings."
Questioned further on whether he wanted "stay in the EU or do you want to leave", he continued: "Investment, jobs, trade and equality, both in or out of the EU I want those things..."
"What we would propose is actually a very good deal, a bespoke customs union with the EU and the trade arrangements would have achieved those things but it didn't go though parliament, that's important."
Labour declined to comment on Ms Thornberry's remarks.