The Belarusian won 6-3 6-2 in 77 minutes to add a third Miami title to her victories in 2009 and 2011.
The 26-year-old has now won 20 career WTA titles and will return to the world's top five next week.
Russian Kuznetsova, 30, was bidding for her second title of the year after her victory in Sydney in January.
Azarenka, a former world number one and twice a winner of the Australian Open, has rediscovered her best form this season after failing to win a WTA title throughout 2014 and 2015.
She began the year with victory in Brisbane in January and last month overcame Serena Williams to win at Indian Wells.
She becomes just the third woman to achieve the Indian Wells-Miami double after Steffi Graf (1994, 1996) and Kim Clijsters (2005).
Victoria Azarenka secured back-to-back WTA titles with a straight-set victory over Svetlana Kuznetsova in the Miami Open final.