Spade was born Katherine Noel Brosnahan in Kansas City, Missouri, the daughter of June (Mullen) and Francis (Frank) Brosnahan, who owned a road-construction company. She was of mostly Irish descent. After graduating from St. Teresa's Academy, an all-female Catholic high school, Spade attended the University of Kansas. She later transferred to Arizona State University. She joined the Kappa Kappa Gamma sorority and graduated with a journalism degree in 1985, thinking she would go into television production. While in college, she worked in sales at Carter's Men Shop, a men's clothing store in Phoenix; her co-worker was Andy Spade, who later became her husband and business partner.