Tanis Philomé was arrested in the Dominican Republic. He has denied any involvement in the assassination of President Moïse on 7 July 2021.
Moïse was shot dead by gunmen who entered his home in Port-au-Prince.
Questions have been raised as to where his security team was at the time.
Haitian police allege a hit squad of mainly foreign mercenaries - 26 Colombians and two Haitian Americans - carried out the killing.
Bullet casings were found strewn across the ground around the property, but the only two people shot were President Moïse and his wife, raising suspicion that some members of security team may have been in on the attack.
The president, who suffered 12 bullet wounds, died at the scene. His wife Martine was seriously injured but survived.
Mr Philomé is the latest in a long line of suspects to be arrested in connection with the case, but the investigation into who ordered the murder has made little progress in the eight months since the assassination.
Dominican officials told the Associated Press news agency that Mr Philomé had been detained by police acting on an international arrest warrant.
He was handed over to the Haitian authorities at a border crossing in Dajabón.