Wozniak, from Blainville, Que., jumped out to a 3-0 lead on Thursday only to see Oudin draw level. The Canadian later broke Oudin's serve to take the first set.
The world No. 118 carried the momentum into the second set to qualify for her second consecutive Grand Slam main draw.
"This match was important for me psychologically," Wozniak said. "I played well and I did what I had to do to qualify for Wimbledon. It feels good to play a lot of matches, it helps to polish my game."
Wozniak joins No. 13 seed Eugenie Bouchard of Westmount, Que., and unseeded Sharon Fichman of Toronto in the women's draw. Milos Raonic of Thornhill, Ont., (No. 8) and Vancouver's Vasek Pospisil (No. 31) are in the men's singles draw.
The 26-year-old Wozniak also advanced to the main draw of the French Open, where she lost to Romania's Sorana Cirstea in the first round.
Wozniak had lost her two previous meetings against Oudin. They were scheduled to play at the Bell Challenge in 2012, but Wozniak was unable to start the match because of a shoulder injury.
She will now get at least three days off before her first-round match. The draw for the singles matches will be made Friday and first-round play is scheduled to begin Monday.
Pospisil was originally unseeded but moved into the No. 31 spot when Nicolas Almagro of Spain withdrew because of a left foot injury.
Almagro was given the No. 25 seed when the list of 32 seeded players was released earlier this week. Players below him all moved up one position except for Russia's Dmitry Tursunov, who remained at No. 32.
Tournament organizers consider player rankings and previous grass-court results over the last two years when determining the seeding, which is why Pospisil was given a higher seed than Tursunov.
Toronto's Daniel Nestor and Serbian partner Nenad Zimonjic are seeded third in the men's doubles draw.
Frank Dancevic of Niagara Falls, Ont., did not qualify after dropping a 2-6, 6-2, 6-1, 6-4 decision to Taiwan's Jimmy Wang.
With files from The Associated Press.