The initiative is being supported by press ads featuring current Miss England and serving soldier Kat Hodge, who became the face of La Senza's Armed Forces campaign last year.
It extends La Senza's established Armed Forces offer which already offers a 15% discount to all British servicemen and women.
This weekend, every shopper who produces their Armed Forces ID at the till point will receive the discount on their purchases.
Model Hodge said: "When you are in the army and you are away from your family so often, it's even more important to keep things special in a relationship. That's why I am so pleased to be the face of La Senza's Armed Forces campaign, this Valentine's."