Italy held the first votes for the EU's next parliament on Saturday, making it the first heavyweight nation to do so.
The EU's 27 member countries, including France and Germany, will vote on Sunday.
Italy, the EU's third-largest economy with 76 seats, could have significant consequences.
Far-right leader Giorgia Meloni cast her vote and stated that the EU election will shape the next five years.
Polling stations have already opened in New Caledonia, with overall results expected late Sunday evening.
The Brothers of Italy party, led by Giorgia Meloni, is projected to win 27% of the votes in Italy's elections, a significant increase from their 2019 score.
Meloni's surge in popularity is part of a broader trend of far-right groups gaining ground across Europe.
Voters like Walter Esposito, a 78-year-old Roman, are turning to Meloni in protest against EU policies, while Carlotta Cinardi, an 18-year-old student, voted for the greens as the most progressive party.
A victory for Meloni could make her a powerbroker in deciding whether EU Commission chief Ursula von der Leyen gets another term.
Giorgia Meloni, the new Italian Prime Minister, is being courted by both European Commission President Ursula von der Leyen and French far-right leader Marine Le Pen to influence EU policies.
However, a European diplomat cautions against viewing Meloni as a kingmaker, as she will primarily focus on Italian interests within the commission and parliament.
Meloni's rise to power in 2022 was driven in part by public concern over immigration, particularly the flow of irregular migrants across the Mediterranean.
EU-wide, immigration remains a contentious issue fueling support for far-right parties.
In the upcoming German parliament elections, the far-right AfD party is predicted to gain around 25% of the seats.
However, the centrist mainstream is expected to still have the most seats.
Tens of thousands of Germans protested against the far-right, with the AfD polling at approximately 15%.
The bigger concern is whether the European People's Party (EPP), led by Ursula von der Leyen, will form alliances with far-right lawmakers.
Von der Leyen has expressed a willingness to work with pro-EU far-right politicians but has ruled out alliances with the National Rally in France or Germany's AfD due to their perceived ties to Russian President Vladimir Putin.
In Slovakia and Italy, two EU countries, right-wing populist parties are hesitant or opposed to providing military and financial support to Ukraine against Russian forces.
Hungary's ruling Fidesz party, where thousands rallied for opposition leader Peter Magyar, is also against helping Kyiv.
In Slovakia, Premier Robert Fico's Russia-friendly camp gained support after an assassination attempt on him, which authorities deemed politically motivated.
Voters like Jozef Zahorsky voted for Fico's Smer-SD party, stating it represents Slovakian interests, not those of Brussels.
Italy was also voting on the same day, with some rallying behind Russia-friendly premier Matteo Salvini's League party.
Fico, the leader of Slovakia's largest party, is against EU arms deliveries to Ukraine to help repel Russia's invasion.
He criticized EU officials as "warmongers" in a
Facebook post.
Fico also shared a photo of himself voting from the hospital and encouraged voters to elect European Parliament lawmakers who support peace efforts instead of war.