Kay was born in New York to a Japanese American mother and a Jewish American father. She began performing poetry at the Bowery Poetry Club in the East Village at the age of 14, joining their Slam Team in 2006. That year, she was the youngest person competing in the National Poetry Slam in Austin, Texas. In 2007 Kay made her television debut, performing the poem "Hands" on HBO's Def Poetry Jam. She has performed at events and venues like the Lincoln Center, the Tribeca Film Festival, and at the United Nations where she was a featured performer for the launch of the 2004 World Youth Report.

Although Sarah Kay works primarily in spoken word poetry, she has had written poems published in magazines such as Foundling Review, DamselFly Press, and decomP literary magazine.