It beat boot-cut jeans to the title in a poll of 3,000 women.
Pull-in pants, which allow the wearer to hide a wobbly stomach, came third followed by stilettos.
Film director Howard Hughes designed a type of push-up bra for Jane Russell to wear in his 1943 film The Outlaw, although Russell later claimed she never wore it.
The little black dress, worn by Audrey Hepburn, mini skirt worn by Twiggy, Sarah Jessica Parker in stilettos and Bridget Jones known for her pull-in pants
In Canada in the 1960s, the Wonderbra was developed and it enjoyed moderate success around the world. But it was not until the early 1990s, when it was marketed with a picture of Eva Herzigova and the words "Hello Boys", that sales started to soar.
Caroline Adams for Debenhams, which polled its customers on their fashion favourites, said: "Push-up bras have become a wardrobe weapon for millions of women across the world.
"It not only makes women feel incredibly sexy but it creates the ultimate cleavage.
Femme fatale: Jane Russell in The Outlaw. Film director Howard Hughes designed a type of push-up bra for her to wear in the 1943 movie, but later claimed she never wore it
"I'm not surprised to see it in the top spot; push-up bras have revolutionised women's lingerie and remain a best-seller instore.
"It's good to see boot-cut jeans and stilettos in the top five fashion inventions - both items are classic wardrobe items and will never go out of fashion."
The push-up bra scooped almost 20 per cent of the vote in the poll.
Boot-cut jeans, which fit perfectly over the footwear and flatter any shape of figure, became trendy in the 1990s.
Sexy stilettos were voted in at number four while the classic little black dress came fifth.
The outfit every girl should have in her wardrobe was shown to perfection by Audrey Hepburn playing the New York socialite Holly Golightly in the 1961 film, Breakfast At Tiffany's.
Hipster jeans came sixth, followed by the mini skirt, strapless bra and support tights.
Other fashion items to feature in the top 20 include stockings at 11 and the G-string at number 12. The bra-boosters known as chicken fillets also made it into the top 20, in 15th place.
Caroline Adams added: "Fashion items that can help create the perfect silhouette have become must-have items for women and there is no shame in faking the body beautiful."
