It was a case of third time lucky for the 30-year-old playmaker, who was also nominated for the award in 2017 and 2018.
Tuwai was a key figure as Fiji won titles in Cape Town, Hamilton, Hong Kong, London and Paris to secure the 2018/19 World Series title, their first since 2016, and was named in the World Series 'Dream Team' for the third year running.
The Olympic gold medallist is the first Fijian player to win the award since Samisoni Viriviri in 2014.
He said Fiji's sevens success is a group effort.