Safin told Russian sports agency R-Sport that his younger sister looks at her decision "as a next step in her life."
"Dinara has decided to end her career," Safin said. "She has taken the decision relatively well. Everything is all right with her health. She feels good in everyday life, but (the back injury means) she simply can't play tennis professionally any more."
The 25-year-old Safina joined the pro ranks in 2000 and captured 12 WTA titles. She reached No. 1 in April of 2009 and spent 26 weeks atop the rankings.
Safina suffered a back injury in 2009 and was outside the top 20 by the end of 2010. She decided to take an indefinite break from tennis back in May, hoping to overcome her back issues.
She dropped to No. 129 in the world.
The three-time Grand Slam runner-up went 12-12 in her career singles finals. She was the runner-up at the 2008 and 2009 French Opens and the 2009 Australian Open and was also a runner-up at the 2008 Summer Olympic Games in Beijing.
Safina's last title came two years ago in Slovenia.
The Moscow native Safina and Safin are the only brother-sister combination to achieve No. 1 status in professional tennis.