The U.S. No. 2 seed had saved match point in her semifinal against Safina's compatriot Elena Dementieva but rarely came under pressure after winning the first set 6-0 in 22 minutes.
The Russian No. 3 fought back, breaking Williams' serve in the first game of the second set, but the American was too strong, taking the match 6-0, 6-3 in 59 minutes.
Williams won the doubles title with her sister, Venus, on Friday, and will regain the WTA world No. 1 ranking when the list is published next week. She has won the Australian Open every other year since 2003 and becomes just the seventh woman to win 10 Grand Slam titles.
Safina's defeat was a disappointing end to a championship that saw three Russians in the semifinals. Williams' last three matches were against Russian women, as she overcame Svetlana Kuznetsova in the quarterfinals.
On a brighter note, Russia could celebrate a win in Melbourne even before Safina took the court, as 17-year-old Ksenia Pervak won the Junior Girls' Singles competition 6-3, 6-1 against Britain's Laura Robson, 15.
