The incident took place in the city of Sarafand (Sarepta) in early hours of Wednesday when armed men shot dead Jamo, who was a pro-Syria politician, and two people accompanying him.
Security sources said Jamo, 44, was fatally shot at close range by an automatic assault rifle inside the sitting room on the ground floor of his three-story house in the city.
The Lebanese security forces have launched an investigation into the incident.
No group has yet claimed responsibility for the attack, but supporters of terrorist groups fighting Syrian troops are top suspects.
Reports say security forces detained two men, a Syrian and a Lebanese, in relation to the terror act.
Jamo was a commentator who worked for Syrian state media and often appeared on Arab TV channels.