[4] In the 1990s, Otegi started his political career and quickly gained prominence within the Basque separatist movement, becoming the leader of Herri Batasuna.
During the period, he participated in the attempts at finding a political and negotiated solution for the Basque conflict that laid out the grounds for the Lizarra-Garazi Agreements and ETA's truce in 1998.
[5] He headed the party Batasuna, declared illegal in 2003 due to its relationship with ETA,[6] but continued talks with the Socialist Jesus Egiguren to reach a compromise leading to peace.
[12] Otegi was chosen as candidate for the post of Lehendakari by EH Bildu for the Basque parliamentary election of 2016 but the electoral committee invalidated his candidacy due to his penal disqualification.
In November 1997, the Spanish Supreme Court found 23 senior members of Herri Batasuna guilty of collaboration with ETA, imprisoning them for seven years.
[16] The ensuing power vacuum was filled by Joseba Permach and Arnaldo Otegi, chosen to become the new provisional leaders of Herri Batasuna.
In the chapter Keys to the resolution it says: "A resolution will not involve any specific impositions, will respect the plurality of Basque society, will place every project on equal terms, will deepen democracy in the sense of giving to the citizens of the Basque Country the last word on the shaping of their future, and that their decision should be respected by the countries involved.
The Lizarra-Garazi agreements helped give Euskal Herritarrok their best electoral results in ten years, and they became the third-largest political party in Basque Country and the adjacent region of Navarre.
Shortly afterwards, a Spanish Supreme Court ruling confirmed the 15-month prison sentence against Otegi for "glorifying terrorism" in a case brought against him for a speech he had given in 2003 in commemoration of the killing of a prominent ETA member 25 years previously.
Meanwhile, starting in October 2007, Otegi was prosecuted along with Pernando Barrena and other former members of Batasuna, PSE political leaders Patxi Lopez and Adolfo Ares, as well as the then incumbent Basque Autonomous Community president Juan Jose Ibarretxe,for holding talks to find a compromise leading to peace, as opposed to the approach adopted by the judge of the Justice High Court of the Basque Country, who considered the meetings illegal.
[32][33] On 16 October 2009, Otegi and several other Batasuna members were arrested and put on trial for their participation in the discussion that would pave the way for ETA's permanent ceasefire.
[34] In March 2010 the Spanish court sentenced Otegi to two years in prison for "glorifying terrorism" in a speech he gave in 2005 in which he compared an imprisoned ETA member to Nelson Mandela.
[35] In September 2010, Otegi again faced trial for glorifying terrorism, this time at a November 2004 rally held in the Anoeta Velodrome in San Sebastián.
He was found not guilty by the Spanish National Court, which ruled that Otegi did not praise ETA, but was defending "peaceful coexistence and the need for a process of dialogue and negotiation in order to resolve the conflict in a non-violent and democratic way".
"The president of the Basque Autonomous Community Iñigo Urkullu declared that it is "about time to stop tampering with the judiciary in order to condition politics".
[45] Despite the sentence, Pablo Casado, leader of the main opposition party in Spain PP, stated all the same that Arnaldo Otegi "should apologize for what he did".
A spokesperson of the interior ministry of Spain denied any involvement;[49][50] other Spanish authorities dismissed the possibility of revealing CNI's alleged participation on the grounds that the activity of the state's spy agency is secret.