Williamson scored four test centuries in the judging period, which began after the World Cup final and finished after this week's 2-0 home test series loss to Australia.
In 2015, Williamson set a New Zealand record for the number of test runs (1172) and centuries (five) in a calendar year, and briefly become the world's No1-ranked test batsman before Christmas.
Williamson is a man of acute modesty but his performances spoke for him during the judging period.
He scored 1003 test runs at 62.68 in nine matches; 980 ODI runs at 54.44 in 19 matches and 404 T20 runs at 57.71 and a strike rate of 138 in nine matches.
With 13 centuries before turning 26, he joined the select group of Sachin Tendulkar, Don Bradman, Alastair Cook and Garry Sobers to have scored as many or more by the same age.
The quality rather than quantity of runs made Williamson's contribution special. He played with technical perfection, inspiring the country's fans.
NZC's annual celebration of cricket - at Auckland's ANZ Viaduct Events Centre - saw McCullum formally farewelled and presented with his International Cricket Council spirit of cricket award.
Others to be recognised included Trent Boult, who was presented with the Winsor Cup for first-class bowling, Martin Guptill was ODI and T20 player of the year, White Ferns captain Suzie Bates was international women's player of the year and Sophie Devine was recognised for her world record fastest 18-ball T20 half-century against India. Amy Satterthwaite was domestic women's player of the year.
Auckland chairman and Cornwall club stalwart Rex Smith received the Bert Sutcliffe Medal for outstanding services to the sport.
The ceremony drew more than 400 invited guests.
