She was awarded the honour at the festival's annual meeting in Dunedin on Thursday.
"This is really great, a real surprise," she said when receiving flowers and a certificate.
"The International Science Festival is one of my loves ... it has taught me that a bit of enthusiasm can get the average person without a science background up there hands-on doing it."
Prof Fleming was nominated for the award in recognition of her outstanding services to the New Zealand International Science Festival since its inception as an incorporated society in 1997.
She followed in the footsteps of Dame Elizabeth Hanan, who was awarded the festival's first life membership in 2010.
Prof Fleming is a professor of science communication at the University of Otago's new Centre for Science Communication, where she convenes the Popularising Science MSciComm.
Science Festival president Mike Harte said Prof Fleming's drive and determination to see the festival succeed were key factors in the society's award to her.
"Jean's energy, her constant stream of fresh ideas for speakers, outstanding international contacts and her own reputation as a scientist and science communicator has made a huge contribution to the success of the New Zealand International Science Festival."
This year's festival, to be held from June 30 to July 8, will take a different approach from previous years, with numerous hands-on events based around the theme "What makes us tick?".
