Speaking on the special edition of the BBC programme, the Labour leader said he would deal with threats “earlier by negotiations and talks”.
He said: “We would not use it as first use and if we did use it millions are going to die – you have to think this thing through.”
The remarks sparked groans from the audience with one man ripping into the Labour candidate.
He said: “Would you allow North Korea or some idiot in Iran to bomb us and then say ‘ooh, we’d better start talking’? You would be too late.”
The man launched a scathing attack Jeremy Corbyn over his stance on Trident
Would you allow North Korea or some idiot in Iran to bomb us and then say ‘ooh, we’d better start talking’? You would be too late
Question Time audience member
The swipe comes after another audience member said: “I find it incredibly concerning that you wouldn’t ever commit to doing that. It’s our safety that you have to look out for first and foremost.”
Presenter David Dimbleby also accused the politician of “dodging the question” and of talking about an “ideal” scenario rather than the “reality” of a nuclear threat.
Mr Corbyn said: “I would do everything I can to ensure that any threat is actually dealt with earlier on by negotiations and talks.
“The idea of anyone ever using a nuclear weapon anywhere in the world is utterly appalling and terrible.”
Snap election 2017: The pictures politicians may not want you to see Sat, May 27, 2017
Protests, fights and daleks, it's all happening as the politicians hit the campaign trail for the snap election
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Jeremy Corbyn during a visit to Hackney Marshes Football Pitches, to highlight Labour's manifesto commitment to ensure 5% of the Premier League's television rights income is diverted to the grassroots game, during a General Election campaign
When asked if would ever fire Trident “under any circumstances”, Mr Corbyn said: “The most effective use of it is not to use it, because it’s there.”
He later added: “If we did use it, millions are going to die – you have to think this thing through. I will decide it on the circumstances of it at the time.”
Among the hostile audience members was one woman who jumped to the defence of Mr Corbyn.
She said: “I don’t understand why everyone in this room seems so keen on killing millions of people?”
Following the grilling, Foreign Secretary Boris Johnson said the Labour leader “would not defend this country”.
He said: “When it came to Jeremy Corbyn on the defence of our country, we have invested £31billion in the Trident nuclear programme and he absolutely refused to confirm that he would even use it.
“Thereby voiding the logic of deterrents, he would not stick up for or defend this country.”