The 26-year-old triumphed over runner-up Porsche Briggs in the live final of the CBS show tonight.
She received the most votes from the show's seven-member jury to grab the $500,000 grand prize, with former houseguests Shelly Moore, Jeff Schroeder, Jordan Lloyd and her fiancé Brendon Villegas all voting to give her the victory.
> Read our full recap of Big Brother's finale episode here
Reilly also triumped earlier in the night by winning the final Head of Household competition, after which she chose to eliminate Adam Poch and bring Briggs with her to the final two to face the panel.
The cocktail waitress from Las Vegas also competed in season 12 of the reality show, where she was evicted on day 36 of the competition.
While making her final speech, Reilly pointed out the multiple competitions she won this season, including three Head of Household titles as well as several Power of Vetos throughout the game.
Briggs walked away with a $50,000 runner-up prize, while Jeff Schroeder secured $25,000 after being voted the fan favourite.
Big Brother airs on CBS and was recently renewed for its 14th season
> Read Digital Spy's full Big Brother headlines