The badly bleeding Bahujan Samaj Party (BSP) leader was declared dead at a hospital after the attack in Shrikanthpur area. The assailants escaped.
Chaubey had lost the 2012 assembly elections from Sakaldeeh (Chandauli) constituency to BJP's Sushil Singh.
Considered close to jailed mafia don Brajesh Singh, the slain man was active in local politics and was considered a frontrunner for a BSP ticket in the 2017 assembly polls.
After the killing, BSP supporters and his neighbours and family members raised slogans against the police and the Samajwadi Party government in the state.
Only last month, a BJP corporator was shot dead in Varanasi, the Lok Sabha constituency of Prime Minister Narendra Modi.