"We are announcing the dissolution of Batasuna," two members of the party, Maite Goyenetxe and Jean Claude Aguerre, told journalists in Bayonne, the main city in France's Basque region.
The move comes after ETA in 2011 announced it had abandoned violence following a four-decade campaign for an independent homeland that claimed more than 800 lives.
ETA has said it is ready to disband under certain conditions.
"We affirm that we will achieve the project of building Euskal Herria (the Basque Country) only by political means, in the face of the oppressive French and Spanish states," Goyenetxe said.
The traditional Basque homeland straddles the French and Spanish borders and Batasuna had remained active as a legal political party in France after it was banned in Spain.
In Spain, former members and supporters of Batasuna have instead rallied around a left-wing separatist coalition, Euskal Herria Bildu, which was created last year.
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The coalition came second in regional elections in October, winning 21 seats while the conservative Basque Nationalist Party, which wants greater autonomy for the northwestern Spanish region, took 27.
A French Basque activist, Aurore Martin, was released on bail in Spain on December 22 after being held on charges of participating in a terrorist organisation, after she allegedly took part in public meetings in the country as a member of Batasuna.