The defections mean that Geert Wilders' Freedom Party (PVV) is no longer the biggest opposition force in the 150-seat house of representatives.
Seven Dutch lawmakers resigned from Geert Wilders' far-right Freedom Party (PVV) on Tuesday to form their own faction, dealing a significant blow to the controversial anti-Islam firebrand who narrowly missed out on victory in last year's national elections.
In a statement on X, Wilders said: "A black day for the PVV. But we always keep going. For the Netherlands. And the sun will shine again."
Wilders told reporters in parliament that the departing lawmakers were not happy with his plan to pursue a policy of "hard opposition" to the new government once it is finalised.
The defections mark the biggest challenge to Wilders' grip on the party since it was founded in 2006. As a result, the PVV is no longer the largest opposition force in the 150-seat house of representatives.
The PVV won 26 seats in the October election, the same number as the centrist D66, which received a slightly larger share of the popular vote and is currently leading negotiations to form a three-party minority ruling coalition government.
Other parties in the splintered Dutch legislature have pledged to work constructively with a minority administration that looks likely to be formed by D66, the Christian Democrats and right-wing People's Party for Freedom and Democracy.
The seven departing lawmakers plan to set up their own bloc in parliament, led by veteran PVV lawmaker Gidi Markuszower.
National broadcaster NOS cited Markuszower as saying that the lawmakers "tried to start a discussion" within the PVV following the last election but that it "wasn't possible."
Wilders, sometimes referred to as the Dutch Donald Trump, is known for his hardline anti-immigration stance and outspoken criticism of Islam. In 2014, he was convicted of insulting Moroccans after remarks he made at an election night rally.
The longest-serving member of the house of representatives, Wilders has lived under round-the-clock protection for more than two decades due to repeated death threats.