Machar’s wife, Defence Minister Angelina Teny, and “a number of his office staff and bodyguards” have also been infected, according to a statement posted on the office’s Facebook page and attributed to press secretary James Gatdek Dak.
Machar “has issued a public statement declaring that he is found positive, and from today will self-quarantine in his residence for the next 14 days,” the statement said.
South Sudan, which is emerging from a devastating six-year civil war, has so far recorded 339 cases of COVID-19 and six deaths, according to the latest figures from the health ministry, also released Monday.
Although the number is relatively low, only 3,908 tests have been conducted.
Aid agencies have been sounding the alarm over a sharp rise in cases in recent days.
Last week, officials announced the virus had reached a camp of some 30,000 displaced people who have been seeking United Nations protection in the capital Juba since 2013. Two cases have been confirmed there.
A case has also been confirmed in a similar camp in northern Bentiu, home to almost 120,000 people.
The country continues to be gripped by humanitarian emergency and hunger, even after Machar and President Salva Kiir — the main rivals in the civil war — formed a unity government in February.
The two men remain deadlocked on key issues such as the control of regional states.
Until last week, Machar had been serving on a task force intended to combat the coronavirus.
But on Friday Kiir dissolved the taskforce, removing a number of politicians including Machar.
The statement released on Monday from Machar’s office said: “a number” of other former members of the task force had also tested positive.
It said Machar was “healthy and with no symptoms.”