The document was published a day before an worldwide conference in the Basque-French city of Cambo-les-Bains to ratify the farewell to arms of an organization founded in 1959, during the Francisco Franco dictatorship (1939-1975).
The director of the Spanish branch of Amnesty International, Esteban Beltran, said ETA's disappearance "does not reduce one bit" the group's responsibility to help clear up its unsolved crimes.
"ETA wishes to end a cycle of the conflict between the Basque Country and the Spanish and French states", it said.
ETA said it has "completely dismantled all of its structures" and will "no longer express political positions, promote initiatives or interact with other actors".More news: Check Out New Footage of Beyond Good & Evil 2's Characters and Spaceships
ETA announced its decision to end attacks in 2011 and in 2017 it handed over 3.5 tonnes of weapons, bringing Western Europe's last major militant campaign to a close.
ETA had already announced that it would be fully disbanding in a letter leaked Wednesday and addressed to various groups and figures involved in recent peace efforts.
Government spokesman Inigo Mendez de Vigo said Spain would continue to pursue suspects in crimes attributed to ETA. ETA can announce its dismantlement but neither its crimes nor the prosecution and punishment of them will disappear.
"Here we have all lost".More news: Europeans push to salvage Iran deal but work on plan B
Following a week of rumours and speculation that the group was preparing to formally declare its dissolution, the announcement was made at the Centre for Humanitarian Dialogue (HD) in Geneva. Last month, it apologized to its victims and their relatives.
The final chapter in the gradual demise of ETA, which was formed in Madrid in 1959 by students angry at the repressive dictatorship of General Francisco Franco, was met with some relief but also resentment.
Violence escalated in the 1960s and Franco's regime responded in kind, as the group assassinated politicians and officials as well as bombing public places.
ETA's announcement was rejected by victims' groups, who argue the separatist group should first and foremost condemn its history of violence and shed light on more than 350 unsolved crimes.More news: Southwest Airlines flight makes emergency landing due to cracked window
But as Spain returned to democracy after Franco's death in 1975 and the Basque Country gained a large measure of autonomy, its attacks on the general populace, including a 1987 vehicle bomb at a Barcelona supermarket which killed a pregnant woman and two children, horrified people and cost it support.