Both were recognised for their community service.
Globally renowned for his portrayal of Lieutenant Hikaru Sulu, helmsman of the starship Enterprise in the original Star Trek TV series, the 85-year-old Takei has also appeared in more than 40 feature films and hundreds of TV shows.
Away from the screen, he served as the spokesperson for the Human Rights Campaign's Coming Out Project and was cultural affairs chairman of the Japanese American Citizens League.
Takei was on the board of the Japan-United States Friendship Commission under President Bill Clinton and remains chairman emeritus of the Japanese American National Museum's board of trustees.
University of South Australia vice chancellor David Lloyd said Takei remains a creative icon and social justice leader.
"George has a unique ability to portray and connect with people of different backgrounds, circumstances, and generations," Professor Lloyd said.
"While so many of us know and love him as a talented actor, he is also a powerful human rights activist, representing the voices and concerns of under-represented groups all around the world.
"George's determination to make a difference to the lives of so many - particularly to those in the LGBTQIA+ community - and his understanding of the role that education plays, is exemplary."
Barnes shot to fame after joining Cold Chisel in 1974 and forged an impressive solo career after the band broke up ten years later, releasing 20 albums and three autobiographical books.
Prof Lloyd said the 66-year-old's life has been defined by perseverance and tenacity.
"From working-class boy to working-class man to working-class hero, Jimmy has had to overcome adversity and countless setbacks, bouncing back stronger each time," he said.
"If you want a gold standard for the unstoppable career, then Jimmy Barnes is it."
The singer said he was both humbled and proud to receive an honorary doctorate.
"The magnitude of this occasion has only just sunk in. I can't stop smiling," he said.
The doctorates were presented on Wednesday, along with those to South Australian landscape artist Geoff Wilson and businessman and philanthropist Andrew Pridham.
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