A statement by Lt. Gen. Abdulaziz al-Shalal was posted on YouTube, The Guardian reported. His location was not disclosed and the date of his defection was not clear, but some rebel sources told the British newspaper he was in Turkey.
"The army has destroyed cities and villages and has committed massacres against an unarmed population that took to the streets to demand freedom," he said. "Long live free Syria."
The BBC said al-Shalal had been suspected of aiding rebels since the uprising against President Bashar Assad's government began in March 2011.
In Syria, the Chinese ambassador, Zhang Xun, called for a negotiated peace between Assad and the rebels, Xinhua, the official Chinese news agency, said. Zhang met Wednesday with Lakhdar Brahimi, the joint envoy of the African Union and United Nations.
"China has always called for a political solution to the Syrian crisis and we will continue coordination and support to Brahimi's mission," Zhang said.
Also Wednesday, Syrian officials were en route to Moscow for talks with the Russian government on ending what has become a civil war, the Guardian said.
The Syrian Network for Human Rights said its daily count of casualties listed 156 people killed across Syria Tuesday, including 10 children and eight women. The violence was the heaviest in the Damascus area, where 55 fatalities were reported.
An estimated 40,000 people have been killed since the uprising began.