The elder Williams has been a regular here for the last three years, winning the event in 2015 after the reaching the final a year earlier.
With reports that the ASB Classic are also close to reaching a deal with Caroline Wozniacki and Ana Ivanovic, it gives next year's event an unprecedented level of star quality.
It's also a bit of a surprise, as the Williams sisters often don't play at the same tournament outside Grand Slams and Premier Mandatory events like Indian Wells and Miami.
"It really is incredible," said tournament director Karl Budge. "I couldn't believe it when we signed Venus four years ago for the first time. To have them both coming is absolutely mind blowing for an event of our size. It really goes to show how respected we are."
Despite turning 36 this year, Venus is still a force on the WTA Tour. She is established inside the top 20 (currently world No 15) and won her 49th career title in Taiwan this year.
She also reached the semi-finals of Wimbledon and made the final of the Stamford WTA event.
"I really love playing in Auckland," said Williams. "This will be my forth year and it has become a special place for me. It is a really nice crowd to play in front of and always full. I have fond memories of winning a title and reaching another final there. I hope I can repeat this in 2017".
