Steyn has been hampered by injuries and missed the ICC World Cup 2019 due to a shoulder injury.
He announced his retirement from Tests but is keen to perform in white-ball cricket.
This BBL stint could help Steyn.
Steyn has said he is still desperate to represent his country in international cricket.
"Obviously the first prize is always to play for your country. Representing South Africa is the only thing I've ever done for my whole career so far, so to get back into that team is prize number one," said Steyn to ICC.
"They're pretty tight on not allowing players to go and play in the Big Bash, but knowing that I'm not available for the Tests, wanting to keep me fit, and also having one eye on the Twenty20 World Cup at the backend of next year, they probably felt like it was a good call," added Steyn.
He wants to gain experience by playing here.
Steyn, who has played 44 T20Is and has featured in the Indian Premier League, will be available for the Stars' first six matches, which also includes the Melbourne Derby.
Steyn said he was looking forward to his stint.
"I'm very excited to join the Melbourne Stars. Having watched closely from afar, the BBL is a top tournament which has a great reputation overseas. I love cricket and want to make a difference in any team that I am playing for," he said.
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