Jeremy Corbyn told his shadow cabinet Labour would launch the "most ambitious and radical campaign for real change our country has ever seen" now a no-deal Brexit was "off the table".
It comes ahead of the Government's bid to convince MPs to back a poll on December 12.
Mr Corbyn told his top team on Tuesday morning: "I have consistently said that we are ready for an election and our support is subject to a no-deal Brexit being off the table.
"We have now heard from the EU that the extension of Article 50 to January 31 has been confirmed, so for the next three months, our condition of taking no-deal off the table has now been met.
"We will now launch the most ambitious and radical campaign for real change our country has ever seen."
Boris Johnson will attempt to convince the Commons to vote for a December 12 election at his fourth time of asking on Tuesday using a short Bill which sets aside the Fixed-Term Parliaments Act, requiring only a simple majority of MPs.
However the Liberal Democrats and the SNP are reluctant to accept his date - fearing it allows time to bring the Withdrawal Agreement Bill before MPs ahead of the start of the campaign.
They have previously signalled support for a poll on December 9, but could put forward a proposal for an election on December 11 - which the Government is likely to accept.
A Number 10 source said: "If there's an amendment to the 11th we could accept."