After graduating from Vassar College, London started her career as a fashion editor at Vogue and transitioned into being a stylist for celebrities and designers.

[1] Her mother, Joy Weinman, worked as a venture capitalist, and her father, Herbert London, was the president emeritus of the Hudson Institute.

"[4] While going to Vassar College, she double majored in 20th-century philosophy and German literature and was a member of Phi Beta Kappa.

[5] It was during a summer internship in Paris in Christian Dior's PR department that she took a serious interest in pursuing a career in the fashion industry.

[6] London has styled for celebrities such as Kate Winslet and Liv Tyler, and on fashion shows for designers Rebecca Taylor, Ghost, and Vivienne Tam.

[6][7] London has worked on numerous advertising campaigns; her client roster includes Hanes, Wonderbra, Bali, Procter & Gamble, CoverGirl, Suave, Target, Levi Strauss & Co., Maytag, Swatch, Longines, and Calvin Klein.

[10] In a What Not to Wear "Best of 2005" look-back show, Clinton Kelly teased London by saying "...there are almost as many great moments as there are high heels in Stacy's wardrobe.

[12] London has done fashion reporting for Weekend Today, The Early Show, Good Day Live, and Access Hollywood.

[17] In addition to her hosting duties and endorsements, London and business partner Cindy McLaughlin co-founded Style for Hire—an online service that matches people with personal stylists that live in their area.

"[26] In January 2015, TLC announced that London would host Love, Lust, or Run, a show similar to her previous work, What Not to Wear.

[33][34] Due to her experience growing up, she became a spokesperson for the National Psoriasis Foundation in 2007[35] and AbbVie's "Uncover Your Confidence" campaign in 2013.

[41] That same year, she performed in the Off-Broadway play Love, Loss, and What I Wore, a series of monologues about women's clothes and their relationship to life events/memories.

[42] In December 2016, London underwent spinal fusion surgery to correct a chronic back problem, which required a six-month rehabilitation.