Christos Pappas, described by prosecutors as Golden Dawn's No. 2, turned himself in to police in Athens yesterday.
Like five other Golden Dawn politicians now in custody, Mr Pappas will be formally charged with membership in a criminal organisation with intent to commit crimes, in an escalation of a government crackdown after a fatal stabbing blamed on a supporter.
It is the first time since 1974 that sitting members of a Greek Parliament have been arrested.
The arrests underline the government's efforts to stifle the fiercely anti-immigrant party, which has been increasingly on the defensive since the killing.
The government ordered an investigation into Golden Dawn's activities after the death of rapper Pavlos Fyssas on September 18 sparked outrage across Greece.
The suspect arrested over his death admitted he had stabbed the 34-year-old and identified himself as a Golden Dawn supporter. Police investigated his mobile phone records and those of 300 people linked to Golden Dawn.
The Golden Dawn deputies can be prosecuted without Parliament needing to lift their immunity.