Siriano first gained attention after winning the fourth season of American design competition show Project Runway in 2007, becoming the series' youngest winner.

[9][11] As a child, Siriano studied ballet,[9][11] and on a March 2008 Ellen appearance, he described himself as a "musical theater kid who loved costumes".

[5] After being rejected by the Fashion Institute of Technology,[13] Siriano chose to study abroad at American InterContinental University in London, England.

[5] Following the recommendation of a teacher during his senior year, he began interning at Vivienne Westwood, and later, at Alexander McQueen,[5] who Siriano has stated was his favorite designer.

[6] Before auditioning for Project Runway, Siriano worked as a freelance make-up artist and made wedding gowns for private clients[9] while also holding a brief intern position at Marc Jacobs.

[19] In 2008, shortly before debuting his fashion line, Siriano began collaborating on several mass market retail collections.

[20] On December 4, 2008, it was announced that Siriano had signed a deal to design a line of low-cost shoes and handbags for Payless ShoeSource for retail in Fall 2009.

[26][27] In 2010, Siriano was named one of Crain's Top 40 Entrepreneurs Under 40, which reported that his line had brought in over $1.2 million in revenue as of 2010[update].

The store launch included celebrity guests like Heidi Klum, Allison Williams from HBO series Girls, stylist Brad Goreski, and DJs The Misshapes.

[35] The New York City show featured a diverse set of models, including Ashley Graham, Selma Blair, and Danielle Brooks, and was attended by celebrities Cardi B, Meg Ryan, Laverne Cox, and Whoopi Goldberg.

[36][33] In 2020, amidst the COVID-19 pandemic, Siriano and his fashion team volunteered to sew face masks for medical professionals.

[37] Siriano began to receive pop culture attention during his time on Project Runway, primarily for his asymmetrical upswept hairdo and his flamboyant attitude.

[11][38] On May 1, 2008, Siriano appeared as himself on season 2 episode 15 of Ugly Betty, and designed some of the cast's costumes (including Amanda Tanen's blouse, which was sold in an auction on the internet).

Upon hearing the news, Siriano posted a warning on his social media accounts: "fyi girls i have never and do not ever look for models on craigslist or online.

[43] In March 2008, Margaret Price, a columnist for Bitch magazine, wrote an editorial entitled, "Is Christian Siriano Making A Hot Mess of the Term 'Tranny'?

"[45] The remark garnered criticism for its derogatory slang and its comparison of transsexuality and drag queen culture to "white-trash" and trailer parks.

[48] Siriano's attorneys released a statement shortly after stating, "It is unfortunate that Designer's Management Agency ("DMA") has commenced a legal proceeding.