While the twin referendums are non-binding, a resounding "yes" vote would give the presidents of the neighbouring regions more leverage in negotiations to seek a greater share of tax revenue and to grab more responsibility from Italy's central government.
Turnout was higher than expected and the results should not be underestimated in the context of the crisis created by Catalonia's push for independence, analysts warned.
Lombardy, home to financial hub Milan, accounts for about 20 per cent of Italy's economy, which is in turn the euro zone's third largest.
Zaia and Maroni are leading members of the anti-migrants, Euroskeptic Northern League party.
The two wealthy Northern League-governed regions, which make up 30 percent of Italy's GDP, are seeking more control over their tax revenues and more say over such policies as immigration, security, education and the environment.
Once the terms are agreed, they will need a green light from parliament in a process that could take up to a year.
'We can now write a new page: The regions that ask for more power will get it, ' Maroni told journalists in Milan.
He said the party was committed to winning greater autonomy for all regions up and down the country.
In Lombardy and Veneto more than 90 percent said "yes "according to preliminary results".
Zaia said the yes victory marked a win for Veneto residents and their civic sense: "Within the framework of the Constitution, we can now work on reforms". No quorum was set in Lombardy, where turnout was lower, above 30pc of the eight million voters.
"Following the populist wave, now Europe has also to face a nationalist/regionalist wave, which somewhat overlaps with the populist one, and makes European integration even more hard", he added.