Mrs May made a statement to MPs about Brexit on Tuesday, amid the threat of a revolt by Remain-supporting ministers.
The PM has promised MPs a meaningful vote on her Brexit deal by 12 March.
But Labour leader Jeremy Corbyn accused the prime minister of another "grotesquely reckless" Brexit delay.
The prime minister said she will put her withdrawal agreement - including any changes she has agreed with the EU - to a meaningful vote by 12 March.
If that fails, MPs will be offered two separate votes:
- One, on the following day, on whether MPs support a no-deal Brexit - so the UK would "only leave without a deal on 29 March if there is explicit consent in the House for that outcome"
- If that fails, then MPs will get a vote by 14 March on requesting an extension to the two-year Article 50 negotiation process to delay EU withdrawal beyond 29 March
"Let me be clear, I do not want to see Article 50 extended," she told MPs.
"Our absolute focus should be on working to get a deal and leaving on 29 March."
Any extension should not go beyond the end of June and "would almost certainly have to be a one-off", she added.
Mrs May said an extension "cannot take no deal off the table", adding: "The only way to do that is to revoke Article 50, which I shall not do, or agree a deal."
Extending Article 50 would require the unanimous backing of the other 27 EU member states and, she said, she had not had conversations about it with them.