De Villiers was unveiled by the Zimbabwe Rugby Union on Wednesday in Harare and he told reporters it was the "greatest day of my life".
Zimbabwe will play a round-robin set of qualifiers for the World Cup with five other African nations, including favourites Namibia, Kenya, Morocco, Tunisia and Uganda.
The top team will be assured of a place in Japan, where they will face New Zealand, South Africa and Italy in Pool B, while the second-placed side will enter the Repechage stage that involves further play-off games against teams from Asia, South and North America and Europe.
De Villiers, known for his out-spoken views on the game, coached the Sprinboks between 2007 and 2011, winning the Tri-Nations in 2009 and a series against the British & Irish Lions that same year.
He was axed after their controversial 11-9 loss to Australia in the quarter-finals of the World Cup seven years ago.
(Reporting By Nick Said; editing by Sudipto Ganguly)
