It is the first time AG Perarivalan has been given parole since his arrest in 1991.
His mother had applied for one month parole for him to visit his ailing father.
The government order, granting him 'ordinary leave' or parole, did not specify the number of days of parole. It also said that strong police escort should be provided to AG Perarivalan during the leave period.
PMK founder S Ramadoss in a tweet expressed happiness at the development.
He said the government would take into consideration the feelings of all concerned and take a decision.
AG Perarivalan and six other convicts have been in prison since 1991, the year a woman Tamil Tiger suicide bomber blew herself up and killed Gandhi at an election rally near Chennai.