It operates in the war-ravaged Syrian city of Damascus and their ongoing battle against President Bashar Al-Assad is reportedly funded by the wealthy nation of Saudi Arabia.
The Arab kingdom has sent millions of dollars to arm and train their fighters so they can defeat the Syrian regime and 'increasingly powerful Jihadi organisations', according to the Guardian.
Known as the Army of Islam, the insurgent group was created in 2011 when Saudi Arabia allegedly engineered the merger of over 50 rebel factions after growing alarmed at the rise if Al-Qaeda and ISIS in Syria.
It is a fierce enemy of both those Islamist groups as well as Jabhat Al-Nusra, but embraces independent rebel forces and 'non-Jihadi' units.
Their graduation ceremony for trainee soldiers in the Ghouta suburb of Damascus was attended by the militants' leadership who watch proudly as their troops march in perfect unison across the expanse.
Jaysh Al-Islam is led by Sheikh Zahran Aloush who addresses the thousands of armed soldiers and tanks once they have assembled on the vast concrete ground below.