The 40-year-old actor and 30 Seconds to Mars frontman can be seen lifting his T-shirt up in one of the black shots to expose his emaciated torso on photographer Richardson's website.
Leto plays a HIV-positive transvestite in The Dallas Buyers Club and recently showed off his facial hair-free face at the 22nd Annual Gotham Independent Film Awards in New York.
The film also stars a skinny Matthew McConaughey, who's shed a huge amount of weight to play Texan electrician Ron Woodroof who contracts AIDS through drug abuse in the late 1980s.
Speaking about losing weight, Leto told Vulture: "Your body goes through weird stages. Sometimes it's hard to hold on to water. But for me, it's not about the most weight I can lose, it's more to represent the character.
"Historically, people have done it for pursuit of self, to achieve a meditative state, so I'm hoping for that. It's not necessarily a bad thing."
See more stars who've lost weight for film roles: