Redouane Sebbar, 25, is suspected of having a hand in the August 2015 attack by fellow Moroccan Ayoub El Khazzani on a high-speed Thalys train travelling from Amsterdam to Paris.
Khazzani, a member of the Islamic State armed group returning from Syria, shot and seriously injured a passenger just after the train had entered France.
He was overpowered by three Americans holidaying in Europe, two of them servicemen in civilian clothing.
Khazzani told investigators he was acting on the orders of Abdelhamid Abaaoud, one of the organisers of the November 2015 Paris attacks, whom he met in Syria.
Abaaoud was killed in a shootout with police days after the Paris massacre.
German investigators believe Sebbar was also a member of Abaaoud's inner circle.
The international warrant for Sebbar's arrest issued on 13 July this year says he is wanted on suspicion of "being part of a terrorist conspiracy" and "complicit in attempted terrorist murders".
French investigators became interested in Sebbar after noticing that he had made a return Thalys trip from Brussels to Paris a few days before Khazzani opened fire on passengers with a Kalashnikov rifle.
Another suspected accomplice of Khazzani's, who was arrested in Germany and handed over to France in April, has already been charged over the Thalys attack.
Algerian national Bilal Chatra, 21, is also accused of playing the role of scout for Abaaoud and Khazzani along the Balkans migrant route into Europe in 2015. He is being held in a French prison.
- with AFP