The incident took place on Friday in Udli village on the Shahganj-Jaunpur road when Lalji Yadav was going in his Scorpio to Jaunpur.
The Scorpio slowed down at the speed breaker when the assailants came from behind on three motorbikes and opened fire.
According to eyewitness accounts, the assailants left only after they were sure that the victim had died.
Lalji Yadav had several criminal cases registered against him. He worked as a contractor in the Akhilesh Yadav regime and took all plum contracts in the district.
Senior police officials reached the spot. The body of Lalji Yadav has been sent for post mortem.
SHO Ramesh Kumar Yadav said that the motive behind the crime could be established only after proper investigations.
This, incidentally, is the fourth attack against the workers of political parties since the Lok Sabha election results were declared on May 23.
A former village head in Amethi, who worked closely with BJP leader Smriti Irani during her Lok Sabha campaign, was shot dead on May 26. Amethi - a bastion of the Gandhi family for decades - voted out the Congress President and Irani was elected.
Earlier, a Samajwadi leader and zila panchayat member, Vijay Yadav, was shot dead in Ghazipur.
On May 27, Samajwadi Party leader and former MP Kamlesh Balmiki was found dead under mysterious circumstances at his home in Bulandshahr district.
( With inputs from IANS )