"The tourism industry was grateful he took the portfolio in 2008 and gave it profile much in the same way that Helen Clark did with culture and heritage."
He had "very capable" associate ministers who were able to support him with the detail of the portfolio.
In 2013 Key boosted the Tourism New Zealand budget by $158 million over three years.
"The big boost to the tourism marketing budget to position New Zealand was welcome. The introduction of the border clearance levy (last year) was less welcome."
Roberts said Key had been personally affected by the letters from relatives of people who had died in adventure tourism accidents.
This had helped lead to a world standard health and safety regime.
Tourism Export Council chief executive Lesley Immink said Key was a charismatic leader and tourism minister and an ''incredible" ambassador for New Zealand.
"New Zealand is firmly positioned on the global stage as an innovative and great country to do business with, that serves to complement our spectacular tourism offerings," she said.
Roberts said he looked forward to Key's successor also being a senior cabinet minister.