She made the declaration during a House of Commons debate
The British Prime Minister Theresa May has said she would be prepared to push the nuclear button to protect the UK - even if it would cause mass fatalities.
She made the declaration as she laid out the case for renewing Trident during a House of Commons debate, ahead of a crucial vote by MPs.
They overwhelmingly voted in favour of renewing the Trident nuclear deterrent.
Some 472 members supported the government's motion, while 117 voted against - a majority of 355.
George Kerevan, an MP for the SNP, asked Mrs May: "Can we cut to the chase? Is she personally prepared to authorise a nuclear strike that can kill a hundred thousand innocent men, women and children?"
She replied: "Yes - and I have to say to you, the whole point of a deterrent is that our enemies need to know that we would be prepared to."
During her first Commons speech since becoming PM, Mrs May criticised Jeremy Corbyn's opposition to maintaining the nuclear deterrent, and described it as a "vital part of national security and defence for nearly half a century".
Mrs May warned the "very real threat" posed by the likes of North Korea and Russia meant it was essential for the UK to have a round-the-clock capability of launching a missile from a submarine.
"We must continually convince any potential aggressors that the benefits of an attack on Britain are far outweighed by their consequences," she added.
Labour leader Jeremy Corbyn was one of those who voted against the deterrent - a stance which is at odds with his own party's manifesto during the last general election.
He said earlier: "I make it clear today that I would not take a decision that kills millions of people, I do not believe the threat of mass murder is a legitimate way to go about dealing with international relations."
The SNP is also strongly opposed to Trident, with the party's Westminster leader Angus Robertson describing it as "an immoral, obscene and redundant weapons system".
After it emerged that 58 of Scotland's 59 MPs had voted against Trident renewal - the exception being the country's only Conservative MP, David Mundell - Mr Robertson warned the "democratic deficit" in Scotland meant a second independence referendum was "fast approaching".
UK Defence Secretary Michael Fallon has estimated the cost of replacing the four nuclear submarines at stg£31bn (€37.1bn) over a 30-year period - with stg£10bn (€11.9bn) set aside as a contingency in case budgets overrun.
The Trident nuclear programme is operated by the UK Royal Navy and based at Clyde Naval Base, commonly known as Faslane, on the west coast of Scotland.