His role as performance coach to the men and women will see him "mentoring and supporting the respective head coaches and enhancing the quality of coaching delivery across the two teams", New Zealand Rugby said in a statement.
A former All Blacks coach, he masterminded the Black Ferns' 2022 World Cup championship run on home soil before stepping down.
He has already resumed work with the women, but will not start with the New Zealand men until after the World Cup this year in France when new head coach Scott Robertson takes over from Ian Foster.
"I have a deep connection and love for any team that wears the black jersey and particularly the Black Ferns and the All Blacks," said Smith, pledging to "challenge norms and encourage coaches and players to think outside the box".
"I also have strong relationships with the respective head coaches and many of the players, so it feels like this role across the two teams is a natural fit."
Smith was named world coach of the year in 2022 and brings vast experience to the role.
After 17 appearances for the All Blacks as a player, he transitioned to coaching and steered the Canterbury Crusaders to Super Rugby titles in 1998 and 1999.
It led to his appointment as All Blacks coach between 2000 and 2001. He has also coached Northampton in England and twice acted as assistant coach to the All Blacks.
"We are very fortunate to have someone of his calibre in our game and involved with our two top national teams," said New Zealand Rugby chief Mark Robinson.
"Smithy's input and insights on the shape of the game and trends in the game internationally will be of enormous benefit to coaches and players.
"But more than that, his integrity, honesty, passion for the jersey and care for the legacy of the black jersey are invaluable."
