"I, General Abdel Aziz Jassem al-Shallal, commander of Syrian military police, announce that I am defecting from the regime army, to join the people's revolution," the military-clad officer said.
"The army has deviated from its essential mission, which is to protect the country, and it has morphed into murderous, destructive gangs," Shallal charged in the video circulated by opposition activists on Wednesday.
"The destruction of cities and villages, and the commission of massacres against our people, defenceless civilians, who took to the streets calling for freedom" prompted Shallal to defect, he said.
Shallal, whose functions are limited to disciplining soldiers, is not a well-known figure.
The Syrian Observatory for Human Rights cited sources close to Shallal as saying he was set to retire in January, and its head Rami Abdel Rahman said he has already left Syria, like many other senior military defectors.
According to reports on online platforms, he left Syria for Turkey.
"This man was pushed to the sidelines a long time ago," one Syrian activist said online, adding that Shallal was "suspected of collaborating with insurgents."
Shallal "withdrew military police checkpoints from the roads, and he was good to people," another activist wrote online.