Gordon Brown will lead a final push to stop Britain leaving the EU.
With just 10 days to go until the in-out referendum, the former prime minister will attempt to persuade Labour voters that they have the most to gain by remaining inside the EU.
"From now until 10pm on June 23 we will not rest and I will not stop explaining why nine million Labour voters have most to gain from remaining in the EU," he will say in a speech in Leicester.
Mr Brown - whose late intervention in the Scottish referendum campaign was considered pivotal - will vow to make the "positive" case for a Remain vote.
Britain will be in "pole position" to champion workers' rights and create new jobs when it takes the rotating presidency of the EU in 2017, he will say.
Vote Leave has dismissed Mr Brown's planned intervention as a "hastily cobbled together relaunch".
In other referendum news:
Migration Watch claimed net migration to the UK would run at more than 250,000 a year for at least 20 years if the UK stayed in the EU
Shadow foreign secretary Hilary Benn will make what he calls the "patriotic case" for remaining
Nicola Sturgeon claimed Scotland will be key to preventing a Leave vote