[3] Raj is the son of former Member of Legislative Assembly Janardan Manjhi who earlier represented the same electoral constituency of Amarpur.

Jayant Raj, who was serving as minister for rural works resigned from his post and in the new government formed after coalition of RJD, JDU, Indian National Congress and other smaller parties, Raj was again reappointed minister, this time for Minor Water Resources in Eighth Nitish Kumar ministry.

[7][8] As minor water resource minister, he led establishment of regional registry office in Amarpur to deal with cases of land registration.

It was established in order to reduce the burden on sole registry office located in Banka district headquarters.

[9] In this second term as minister, Raj has also remained a critic of Upendra Kushwaha (a rebel leader of Janata Dal United).