Fourteen other people, including the groom, were injured. The bride was not with the wedding party.
The party was disembarking from a boat at the riverside town of Shibganj, heading towards the bride's house, when they were caught in a thunderstorm.
Local people said several bolts of lightning hit the group.
Every year, hundreds of people across South Asia are killed by lightning.
In 2016, Bangladesh declared lightning strikes a natural disaster when more than 200 people died in the month of May alone, including 82 people on a single day.
Experts say deforestation has played a part in the rising number deadly lightning strikes due to the disappearance of many tall trees that before would have drawn lightning strikes.