French and Moroccan authorities identified the man as 26-year-old Gelel Attar, a Belgian of Moroccan descent.
A spokesperson for the Moroccan Central Bureau of Judicial Investigations said Attar is from Molenbeek, Belgium, and knew the Paris attackers well.
Molenbeek is an impoverished suburb of Brussels with a history of links to terror plots.
It has a large, predominantly Muslim population of first-, second- and third-generation immigrants from North Africa and has gained an unwelcome reputation as a hotbed of jihadism.
Attar was being held in Sale, close to the Moroccan capital, Rabat, the spokesperson said.
His family, which was notified of his arrest immediately after his capture, is not under investigation, according to the bureau spokesperson
Belgium couldn't say for sure whether Attar would be extradited.
"There is an international arrest warrant," said Erik Van Der Sypt, spokesman for the Federal Prosecutor in Belgium. "Normally Morocco does not extradite its own nationals. So we will see. We don't know yet."
A French law enforcement official told CNN that Attar traveled to Syria in 2013 with Chakib Akrouh, a suicide bomber who blew himself up in the police raid on a Saint-Denis apartment, days after the Paris attacks.
Belgian CNN affiliate RTL quoted Moroccan authorities saying Attar also met in Syria with the suspected ringleader of the Paris attacks, Abdelhamid Abaaoud.
The Saint-Denis raid happened four days after alleged associates of Abaaoud killed 130 people and injured hundreds in several locations in Paris and Saint-Denis, a guns-and-explosives attack claimed by the Islamist terror group ISIS.
Attar was convicted in absentia by a Belgian court last year of recruiting jihadists and sentenced to five years in prison, RTL reported.
Police are still looking for Salah Abdeslam, a 26-year-old Belgian-born French national who authorities believe played a role in the Paris attacks but went to Belgium afterward.
A senior European counterterrorism official told CNN last month that the trail for Abdeslam had gone cold.