The co-chairwoman of the nationalist Alternative for Germany party said today she plans to leave it just two days after it made a strong showing in the country's elections.
Frauke Petry's announcement came as other politicians from the anti-migrant party gathered for their first meeting after their breakthrough.
Alternative for Germany, or AfD, won 12.6% of the vote in Sunday's election to win seats in the national parliament for the first time.
Ms Petry, its co-chairwoman since 2015, announced on Monday that she would not join its parliamentary group and other leaders urged her to leave the party altogether.
"It is clear that this step will follow," Ms Petry said on Tuesday in the eastern city of Dresden, in remarks reported by the dpa news agency.
Ms Petry's husband, Marcus Pretzell, the party leader in the western state of North Rhine-Westphalia and a regional politician there, said he is also leaving AfD.
AfD won 94 of the 709 seats in the new German parliament, including Ms Petry's.
It was not immediately clear whether any others would follow Ms Petry, who moved AfD's focus from opposing eurozone bailouts to migration after she took over in 2015 but has been increasingly sidelined in recent months.
Ms Petry has said she was aiming to make the AfD ready for government in 2021, and urged her party earlier this year to exclude members who expressed extremist views.
She said on Monday that "an anarchic party" can be successful in opposition but cannot eye a place in government, before storming out of a press conference and leaving other party leaders momentarily speechless.
Fellow AfD members appeared relatively unconcerned by Ms Petry's departure as they gathered in Berlin.
Asked whether other politicians will follow Ms Petry, co-leader Alexander Gauland said: "I hope not, but I can't look into people's heads."
Sunday's election left Chancellor Angela Merkel's conservative bloc weakened but still easily the biggest group in parliament.
Mrs Merkel now faces a complicated task in forming a coalition, most likely with the pro-business Free Democrats and the traditionally left-leaning Greens.
Her partners in the outgoing government, the centre-left Social Democrats, say they will go into opposition after they lost substantial support in the vote.
Mrs Merkel also faces calls from her own allies for a more robust conservative image.