She made the remarks on Wednesday morning after a confidence vote in her leadership was triggered.
Theresa May has said that her being replaced as Prime Minister would mean a delayed or cancelled Brexit, as she fights for her job ahead of a
vote on her leadership tonight.
The crunch vote will take place after over 48 Conservative MPs submitted no confidence letters in her, triggering a ballot by all of the party's MPs.
Speaking outside Downing Street on Wednesday morning, May said that she intended to contest the confidence vote "with everything I’ve got", adding that she was ready to "finish the job" she began after becoming party leader.
She said: "A change of leadership in the Conservative party now would put our country’s future at risk and create uncertainty when we can least afford it.
"A new leader wouldn’t be in place by the 21 January legal deadline, so a leadership election risks handing control of the Brexit negotiations to opposition MPs in parliament.
"Weeks spent tearing ourselves apart will only create more division just as we should be standing together to serve our country. None of that would be in the national interest."
May also claimed that a new Prime Minister would mean "delaying or even stopping Brexit" as they would not be installed in time to meet January's legal deadline on negotiations.
She argued: "The new leader wouldn’t have time to renegotiate the withdrawal agreement and get the legislation through parliament by 29 March, so one of their first acts would have to be extending or rescinding article 50, delaying or even stopping Brexit when people want us to get on with it.
"And a leadership election would not change the fundamentals of the negotiation, or the parliamentary arithmetic."
She added: "None of that would be in the national interest. The only people whose interests would be served would be Jeremy Corbyn and John McDonnell."
All serving Tory MPs will now be able to cast a vote either for or against May tonight and the Prime Minister will need the backing of at least 158 of them to survive.
Sir Graham Brady, chairman of the 1922 committee, announced the vote on Wednesday morning. He said: “The votes will be counted immediately afterwards and an announcement will be made as soon as possible in the evening."
The ballot will be held between 6pm and 8pm on Wednesday evening.
