Kirby proposed with a 9-carat diamond engagement ring while the couple were dining in Coronado Island, CA on Tuesday.
Brodie told E! News: "I'm thrilled to be engaged to Will. I've loved him for years and he has made me the happiest girl in the world."
The couple, who welcomed a baby son last year, first met while appearing on a Bravo chatshow.
Kirby was crowned Big Brother 2 champion in 2001 after forming the 'Chilltown' alliance with fellow contestant Mike 'Boogie' Malin and escaping eviction four times.
Brodie also appeared as a reality television contestant on the dating gameshow For Love or Money in 2003.
Kirby will compete in the first-ever Reality Mud Run on September 10 to raise money for Stand Up To Cancer.
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Watch Dr Will Kirby deliver his final speech to Big Brother jury voters below: