"Abdel Qader Saleh has been martyred," said a posting on a Facebook page linked to the brigade.
The Britain-based Syrian Observatory for Human Rights also reported the death.
"Abdel Qader Saleh, known as Hajji Marea, died of wounds he sustained last Thursday when war planes targeted the Liwa al-Tawhid leadership," it said in a statement.
"He was taken to Turkey after being wounded, and died in a hospital there before being brought back to Syria for burial," Observatory director Rami Abdel Rahman told AFP.
More From This Section
He had been in a car along with Saleh, and another senior figure in the rebel group, Abdelaziz Salameh, who was also wounded.
Following the attack, Liwa al-Tawhid arrested 30 people suspected of being informers for the regime of President Bashar al-Assad.
Saleh, chief of operations for Liwa al-Tawhid, was widely seen as the brigade's most important figure.
His death comes as the Syrian regime makes new gains in Aleppo, seizing several towns and talking about reopening the Aleppo International Airport after nearly a year of closure.
It does participate in the military command linked to the Coalition, and is one of the best known rebel brigades fighting in the Aleppo area, with Saleh widely known in the region.