Jonathone N Sangma was on his way to constituency when the convoy came under attack.
Sohan D Shira carried a reward of Rs 10 lakh on his head.
Polling will be held between 7 am and 4 pm, except in some polling stations of the interior districts of Nagaland, where the process is scheduled to conclude at 3 pm. The two states have a 60-member House each, but voting will be held for 59 constituencies in both.
Nagaland Chief Electoral Officer Abhijit Sinha said the violence in Akuluto constituency in Zunheboto district left one dead and two injured.