At least four others were killed in the strike, including Chatah’s advisor and bodyguard, and at least 70 were wounded, sources said.
Known for his criticism of Syrian President Bashar Assad, Chatah, a Sunni Muslim, was also an opposition figure and aide to former prime ministers Saad al-Hariri and Rafik Hariri.
Sources at the explosion site said Chatah was on his way to attend a meeting when the explosion occurred.
The explosion was caused by a car bomb and coincided with a meeting of anti-Syrian politicians, according to media reports.
The blast occurred a few hundred meters from the government headquarters and parliament building, near the Starco Center in downtown Beirut. This area is near that where Rafiq Hariri’s convoy was struck in 2005.
The explosion was heard across the city and a plume of black smoke was seen rising in the downtown business district near the Phoenicia Hotel.
The army cordoned off the area to prevent people from getting close to the scene, where the twisted wreckage of several cars was still smoldering. The explosion appeared to be the result of the car bomb, but security officials said they had no immediate confirmation.
Footage broadcast on Lebanese TV showed medical workers rushing the wounded to ambulances. At least two bodies could be seen lying on the pavement.
About one hour before the blast, Chatah tweeted:
“#Hezbollah is pressing hard to be granted similar powers in security & foreign policy matters that Syria exercised in Lebanon for 15 yrs.”
In June, he was quoted by the Associated Press as saying “There’s a general mood of anger and oppression among Sunnis in Lebanon of being lorded over by Hezbollah.”
Lebanon has seen a wave of bombings over the past months as tensions rise over Syria’s civil war.