Singh told PTI he would enter into fray from his traditional constituency Kargahar in Rohtas district on a Samajwadi Party ticket.
"I have resigned from ministry and also JD(U)," Singh, Health minister in the JD(U) government, said.
The minister said he was at loss to understand why he was denied renomination.
In the joint list of grand secular alliance released by Chief Minister Nitish Kumar on behalf of the three constituent parties, Vashishth Singh has been given ticket from Kargahar Assembly seat in place of Ramdhani Singh.
A hurt Singh said Chief Minister Nitish Kumar expressed unhappiness over his functioning.
Asked if he has reasoned with the CM over denial of ticket to him, Singh answered in negative.
Apprehending the worst, a large number of supporters of Singh had assembled outside JD(U) office when Kumar was releasing the list.
The aggrieved supporters shouted slogans against CM as soon as the list was released and Singh's name was missing from it.