Matteo Salvini is the main alliance partner for Giorgia Meloni in a right-wing coalition that is leading opinion polls ahead of Italy's snap general election on Sunday.
His Northern League party is allying with Meloni's far-right Brothers of Italy and Silvio Berlusconi's Go Italy movement.
If the bloc does triumph, it is likely to be a bittersweet moment for Salvini who has seen his position as the right's undisputed leader usurped by Meloni.
"For me, it would be a pride, a joy, a thrill to be chosen by you and President Sergio Mattarella as prime minister of this extraordinary country," Salvini said last week before thousands of flag-waving supporters in Pontida, the spiritual home of his party
Meloni's Brothers of Italy party is forecast to take around 25% of the vote, while the League is seen at around 12%, down from 34% in a European parliament election in 2019.
The Northern League was originally rooted in the wealthy north, with the then leader Umberto Bossi demanding secession from the poorer south.
Salvini, 49, rebuilt the party from near ruin when he took charge nine years ago, replacing the old independence battle cries with the slogan "Italians first" and replacing chants against Rome with insults directed at Brussels.
His strategy appeared to work, with the League forming a coalition government in 2018 and Salvini himself becoming the interior minister. But a series of political blunders since then have allowed his ally Meloni to leapfrog him in the polls.
At the beginning of the rally, ministers and regional governors of the League formally committed to giving greater autonomy to regions and pursuing cuts in taxes and energy bills.
They also promised to lower the retirement age, stop immigrant landings and improve the justice system.
In his speech, Salvini vowed to scrap the €90 tax Italians pay annually to fund the state-owned broadcaster RAI and to revitalize small villages by making them a real estate tax-free zone.