[2] At the time of his election, Lagos was a member of Greek neo-Nazi ultranationalist political party and criminal organization Golden Dawn.

On 7 October 2020, Lagos was found guilty of running Golden Dawn, and a number of other serious offences, including orchestrating the fatal stabbing of Pavlos Fyssas and many violent attacks on migrants and left-wing political opponents.

[5] He has served for a number of years as a member of the Hellenic Parliament for the neo-Nazi party Golden Dawn between 2012 and 2019, and was elected to the European Parliament on the party's ticket before announcing that he would sit as an independent a few days after being sworn in as an MEP on 2 July 2019.

[10] His actions with Golden Dawn have twice led to his arrest and detention on charges of forming a criminal organization, while he is also allegedly involved in the murder of Pavlos Fyssas, which led to his conviction, along with many other members, on October 7, 2020 as one of the leaders of the criminal gang.

[5] On October 19, 2020 Greek authorities submitted a request to the European Parliament to have Giannis Lagos' parliamentary immunity lifted in order to prosecute him.