Major Manaf Talas was one of the heads of the Syrian Republican Guard, a 10,000-member-strong elite body guard unit known for its loyalty to president Bashar al-Assad.
Talas' move to join the opposition in neighbouring Turkey represents one of the highest level defections since anti-government protests started in March 2011.
Death-toll estimates from the violence now widely referred to as a civil war range from more than 10,000 by the United Nations, to more than 14,000 by Syrian opposition groups.
The Syrian government denies reports by the UN and rights groups that it is responsible for most of the violence that began when the Arab Spring protests spread from Tunisia, Egypt and Libya where they toppled those countries leaders.
Assad however claims to have popular support and denies that the uprising in Syria is similar to other Arab countries.
Opposition leaders "wanted to bring mass numbers of people into the public squares likes in Egypt and Tunisia, but they failed," Assad said in an interview with the Turkish Cumhurriyet daily published on Thursday.