The actress was a series regular throughout the seventh season, and later made a guest appearance in the season eight episode 'Bloodline'.
According to Entertainment Weekly, Vandervoort will reprise her role as Clark Kent's cousin Kara in an episode scheduled to air in October.
It was previously announced that John Schneider will also return to the show as Clark's adoptive father Jonathan Kent.
Former stars Kristin Kreuk (Lana Lang) and Michael Rosenbaum (Lex Luthor) have also been rumoured to be making an appearance in the tenth and final season of Smallville.
The show will return to The CW on September 24.