The victory gave the sixth-seeded Williams her 40th career title, but first this season.
"It was a great week to be able to win against the world's best player, my sister," Williams said, referring to her 6-1, 2-6, 7-6 (7-3) semifinal victory Friday against younger sister, Serena.
Venus improved to 3-1 lifetime against her unseeded French opponent, and 7-1 overall in her last eight finals matches.
Razzano, who had beaten top-five players Dinara Safina and Vera Zvonareva earlier, was slowed by back stiffness in the nearly non-competitive second set.
In her previous match with Williams, the 2007 Japan Open final, Razzano pulled off an upset by saving three match points in the second set.