A parliamentary source in Damascus, on condition of anonymity, confirmed that Mujhem al-Sahu from Deir Ezzor province in eastern Syria had been executed, without specifying who was responsible.
The source said 50-year-old Sahu was killed in Deir Ezzor but gave no additional details.
Last month, the Observatory reported that another Syrian lawmaker, Mohanna Faisal al-Fayyad, a Sunni, had been kidnapped by Islamist and jihadist opposition fighters.
The monitoring group said Ahrar al-Sham rebel fighters and jihadists from the Al-Qaeda-affiliated Islamic State of Iraq and the Levant (ISIL) abducted Fayyad on October 27.
He was kidnapped after two days of clashes between members of his tribe, which supports the regime of President Bashar al-Assad, and rebel groups