M5S opposed and criticized the law, with Di Maio telling CNBC that "all Italian parties are trying to defeat us by approving an undemocratic electoral law."
Importantly, the vote could have far-reaching consequences for Italy's fragile economy. Gross domestic product (GDP) grew 0.3 percent in the fourth quarter, a slowdown in growth from the third quarter's 0.5 percent expansion.
The country's banking system is mired in non-performing loans amounting to more than 300 billion euros ($368.5 billion). Italy's debt-to-GDP ratio stood at 133 percent in 2017, according to the International Monetary Fund.
Daniel Lacalle, chief economist at Tressis Gestion, told CNBC on Thursday that Italian politics had a habit of muddling through, but the economy was in a "worrying" shape.
"I think that we need to worry because asset prices in Italy have risen dramatically on the back of the European Central Bank (ECB) support (from quantitative easing) and stronger numbers in the euro zone," he said. "But the Italian economy is not doing well, it's not moving along with Spain and France.
"There's a reluctance in the Italian government and Italian authorities to address the problem of non-performing loans in the Italian financial system and those two elements — the lack of growth and NPLs — continue to be a source of concern."