Williams posted, "Made a very tough decision today..." with an attached link that opened onto a Nets team logo.
Multiple media reports Tuesday put the three-time all-star's new contract at $98 million over five years. He was also being pursued by the Dallas Mavericks.
The news came as the Nets -- preparing for their first season in their new home at Brooklyn's Barclays Center -- are reported to have acquired all-star guard Joe Johnson from the Atlanta Hawks while also re-signing Gerald Wallace.
The 28-year-old Williams came to the Nets in a February 2011 trade with the Utah Jazz. He has averaged 17.6 points and 9.2 assists over 506 career games.
Former Titans kicker dies in car crash
UPI Sports Results for September 20, 2014