The 'Born This Way' singer made her appearance on the runway halfway through Mugler's womenswear fashion show, held at a gym on Wednesday.
The star, who arrived on the catwalk sporting pigtails, smoking a cigarette and dressed in a black ensemble, was modelling fashion from the autumn/winter 2011 collection, created by her stylist Nicola Formichetti.
She had earlier told fans about the appearance, writing on her Twitter account: "I''m so excited I might give birth to a machine gun."
GaGa, who directed the show music, also took the opportunity to preview her new song 'Government Hooker', taken from her upcoming album Born This Way, which is scheduled for release this May.
Formichetti is a member of the singer's Haus Of GaGa collective.
