The top-seeded American claimed a 6-3 6-4 victory in one hour 34 minutes.
Roddick was dominant on serve in the opening set, losing just one point on his first serve.
He was unable to maintain that level in the second, winning just 36% of points on his second serve, but two breaks helped earn him victory.Raonic continued his excellent run in Memphis as he knocked out fourth seed Mardy Fish in three sets in the other semi-final.
The 20-year-old sent down 23 aces, including 10 each in the opening two sets, on his way to a 6-4 4-6 6-3 success.
Slovakia's Magdalena Rybarikova won the Cellular South Cup after her opponent in the final, the sixth-seeded Canadian Rebecca Marino, was forced to retire at the end of the first set.
Rybarikova took the opening set 6-2 and, with Marino unable to play a second, was handed victory.
