The `Born This Way` singer showed her support for the WikiLeaks founder by stopping off at the Ecuadorian embassy in London, where he has been living since June.
Gaga was nearby at department store Harrods promoting her new fragrance The Fame when rapper M.I.A. tweeted her, suggesting: "If ur at harrods today, come visitAssange at the Ecuador embassy across the st. im there. ill bring TEA and CAKE. (sic)"
Assange is claiming asylum at the embassy to avoid extradition after facing rape and sexual assault allegations from two women in Sweden, and he fears extradition to America for publishing sensitive diplomatic information online if he were to return to Sweden.
Gaga stayed in the embassy chatting with the WikiLeaks mastermind for five hours over a private dinner, and finally emerged at midnight to pose for a photo with the fugitive.
The image - which shows Gaga clad head-to-toe in black and wearing a wide-brimmed pointy hat - was uploaded to her official website www.littlemonsters.com with the caption, "no headline".
The 26-year-old star`s fans have been widely supportive of her decision to visitAssange, praising the singer for making a statement in support of freedom of speech.
Gaga - real name Stefani Germanotta - has backed several political campaigns in the past, most notably gay rights in America which recently won her the LennonOno Grant For Peace award.