Malong, a former ally of President Salva Kiir, fell out with him last year and was sacked from his post in May 2017.
He was then held under house arrest for six months.
Despite this, he remains one of South Sudan’s most powerful men – with influence in the military, politics and business.
He is accusing President Kiir and those around him of massive corruption and leading the nation to bankruptcy.
Malong says he intends to bring South Sudan’s security crisis under control and steer the country towards democracy and development.
He wants to join in the next round of talks between the government and opposition, which will be held in Addis Ababa, Ethiopia later this month.
However, he’s making these statements while also announcing a rebel movement.
It’s these ambitions that the government feared last year when it placed him under house arrest, accusing him of planning to mobilise militants for a rebellion.
The UN has also accused Malong of coordinating ethnically-motivated attacks against civilians during South Sudan’s 2013 civil war.