Mr Smith had been a trustee for nine years and assumed the chairman position last February when then-chairman Paul Bowker announced his retirement.
Mr Smith, who is owner-director of Waihi Beach Top 10 Holiday Resort and Beachaven Holiday Park, said during his time on the board he had seen the region's tourism industry continue to go great guns, but acknowledges it is time for a change.
"I've been very fortunate to be part of an organisation that is committed to taking the region from strength to strength, and I know Des will continue to take the organisation and the region in the right direction."
Tauranga mayor Stuart Crosby thanked Mr Smith for his contribution to the region's tourism development in the last few years.
"Ian has provided great leadership to guide Tourism Bay of Plenty into the future and we would like to thank him for his engagement, especially for Tauranga, as well as the wider Bay of Plenty region."
The new chair is also joined by two new board members this month: Peter Moran and Will Wilson.