The model, who has appeared on covers of Elle and French Vogue, said she will solely model women's fashion in future.
"To all trans youth out there, I would like to say respect yourself and be proud of who you are," Pejic told GLAAD magazine.
"All human beings deserve equal treatment no matter their gender identity or sexuality. To be perceived as what you say you are is a basic human right."
Pejic later posted a selfie on Facebook.
"I want to take this opportunity to thank all of you for the love and support throughout the years. You've all helped me through this journey and I have learned a lot and really come into my own and the response to today's announcement truly overwhelmed me and reminds me of why I chose to do this publicly.
"I think we all evolve as we get older and that's normal but I like to think that my recent transition hasn't made me into a different individual. Same person, no difference at all just a different sex I hope you can all understand that," Pejic posted on the social networking website.