Oleksiy Vadatursky, 74, and his wife Raisa died when a missile hit their home overnight, local officials said.
Mr Vadatursky owned Nibulon, a company involved in grain exports. He had also received the "Hero of Ukraine" award.
Ukraine's President Volodymyr Zelensky described Mr Vadatursky's death as a great loss.
Mykolaiv mayor Oleksandr Senkevych said it was probably the heaviest Russian bombardment of the city so far.
There was damage to a hotel, a sports complex, two schools and a service station, as well as homes.
