Venus Williams will join world No.2-ranked sister Serena at the ASB Classic in Auckland early next year.
A five-times Wimbledon champion, 36-year-old Venus is currently ranked 15th in the world.
With seven Grand Slam titles to her name, and four Olympic gold medals, she has been ranked No.1 in the world three times in her career.
Venus Williams reached the semi-finals at Wimbledon this year, where she lost 6-4 6-4 to Angelique Kerber of Germany, who was beaten 7-5 6-3 by Serena Williams in the final.
The Williams sisters have jointly captured 120 WTA Tour titles, 29 grand slam singles and 18 grand slam doubles titles.
Next year's Auckland Classic will be the first time since 1998 the pair have played at the same international level event.
The Williams sisters have played each other 38 times at Tour level events, with Serena edging Venus 27 -11.
The pair are the only women players confirmed for the Auckland Classic, although media reports have suggested former world No.1s Caroline Wozniacki of Denmark and Serbia's Ana Ivanovic are potential starters.
