The decision was made after the SC considered a petition filed by Attanayake challenging the cancellation of his party membership.
The former UNP General Secretary, who pledged support to then President Mahinda Rajapaksa ahead of the Presidential Election in January was made Health Minister for less than three weeks after he defected from the UNP.
He was expelled from the UNP following a decision by its Working Committee.
On February 11, Attanayake was released on bail after being arrested on criminal charges of falsifying a document.
He is accused of fabricating the document to discredit President Maithripala Sirisena and Prime Minister Ranil Wickremesinghe.