Confirmation of a long-suspected move came with an official announcement from the Saudi-backed organisation and on its twitter account.
Compatriot Marc Leishman has also signed up to the new body, the arrival of which has split golf.
They bring the number of Australians on board with LIV to eight with Marc Jones the next biggest name of the octet.
Australian LIV CEO Greg Norman revealed earlier this month the circuit is looking to hold an event Down Under in 2023 and have been scouting potential venues.
Smith and Leishman are among six players joining the circuit in time for it's fourth event, at The International course in Boston, Massachusetts, teeing off on September 2-4.
The other four are Chile's world No.19 Joaquin Niemann, India's highest-ranked player Anirban Lahiri, and Americans Harold Varner III and Cameron Tringale.
Two-time Masters champion and former world No. 2 Bubba Watson will also be making his LIV debut, but as a non-playing captain and pundit.
Smith, 29 from Brisbane, is the first current top-10 player to join LIV. He has had a stellar season winning the Players Championship as well as the Open. He was also tied for third at The Masters, one of three top-5 Masters finishes in the last five years.
His switch to LIV has been long trailed, being first reported in the wake of his Open triumph with a $US100 million ($A145m) signing-on fee mentioned.
Leishman, 38 from Victoria, has won six PGA Tour events during his career. Now ranked 62nd in the world he has reached No.12 in the past and has twice finished in the top five in both the Open and the Masters. However, while he was fifth at the Masters in 2021 he has missed the cut in seven of his last 15 major appearances.
Both players are still eligible for this summer's Australian PGA and Australian Open but will no longer be considered for next month's President's Cup.
The $US25m ($A36m) Boston event features a 48-man field playing 54 holes. Other Australians in the field besides Smith, Leishman and Jones are current Australian PGA champion Jediah Morgan and Wade Ormsby.