Andreja was born as "Andrej Pejic" to a Croatian father and Serbian mother in Tuzla, Bosnia and Herzegovina; left in the 90's with her family from the war ravaged country eventually settling in Melbourne Australia. At the Paris men’s shows in June (2010), the then 19-year- old Andreja became the symbol for fashion androgyny.
In January 2011, Andreja walked for Jean Paul Gaultier in his men's show and for the January 2011 couture show, eventually appearing in the Spring/Summer 2011 JPG campaign with Karolina Kurkova. The same season, Andreja appeared in the Marc by Marc Jacobs campaign. Named one of OUT Magazine's 100 Most Compelling People of 2011. In early 2014, Andreja underwent sex reassignment surgery and came out publicly in July 2014 as a transgender woman, which marked her transition from an androgynous model to a female model.