Karp began writing professionally in 2011 at the age of 10 when Molly McAleer, co-founder of Hello Giggles, asked her to contribute to the website by writing "Ruby's Corner", a weekly column that covered a variety of topics involving her observations and life experiences.
[6] On her third birthday, Karp found herself onstage at UCB as a guest on Talk Show with Paul Scheer and Jake Fogelnest.
In 2004, she appeared on the first episode of Shutterbugs with Aziz Ansari and Rob Huebel on the MTV sketch comedy television show Human Giant.
In 2008, Karp spoke about being a feminist with Amy Poehler on her web series Smart Girls at the Party when she was 7 years old.
Her mother, Marcelle Karp, is a TV producer and a co-founder of the women's lifestyle magazine Bust.