Sunil Kumar was born to veteran Janata Dal (United) leader and parliamentarian Baidyanath Prasad Mahto.

In 2022, after the tragic incident of shootout at the residence of Narkatiaganj based businessman Guddu Barnwal, he announced that he could even lift the weapon to protect his people.

In his parliamentary address given during Zero hour, he drew the attention of the seat of Lok Sabha on the importance of Valmikinagar constituency, given its proximity to Nepal.

According to him, being connected to Sita of Ramayana and harbouring the only tiger reserve of Bihar, presence of a functional airport may boost the tourism potential in the region.

Thereby, in the Piprasi bloc of Bagaha, he was rounded up by the people who complained against the rural works department of Government of Bihar.