Under a deal struck between Smith and CA, he will be added to the Sixers squad as a replacement player once an international star heads back overseas in early January.
Smith will then become available when the Test summer finishes on January 8, allowing him to play up to four regular-season matches.
Ordinarily, the role of a replacement player attracts payments of $2200 per game, but Smith will now receive a greater salary as part of marketing expenditure.
"Steve and his management recently confirmed he will be available to play in this summer's Big Bash, after his international commitments have finished in January." Sixers boss Jonathan Robinson-Lees said. "That is great news for the Sixers, the BBL and for fans.
"We are really excited for the team and especially our fans, who will now get to see one of the world's greatest players in magenta this summer."
Smith's time at the club will include the Sydney Smash against Warner's Thunder at the SCG on January 21. His return will mark the first time he has played in the BBL since 2019-20.
The 33-year-old had attempted to play for the Sixers last summer, but was controversially precluded as he had not nominated for the player replacement pool.
It had appeared as if he would suffer the same fate this summer, after the Sixers filled up their initial roster space believing Smith would not be available.
However, CA bosses met Smith's management during the Perth Test earlier this month in a bid to bring him back to the competition before it was eventually finalised.
The outcome is a major win for CA on several fronts. Smith is a crowd-puller, and one the BBL needs given Glenn Maxwell and Mitchell Marsh have both been ruled out of the tournament through injury.
It also comes after the organisation has been heavily criticised in recent weeks for a failure to make clear decisions, as highlighted by the Warner leadership saga.