Leyster was extremely successful in her day as a portrait and genre specialist. Little is known about her early training but she was mentioned in about about Haarlem as being a local artist. In her early twenties she became the only female member of the Haarlem painters' guild and soon had students of her own. Even though her work is closely identified with that of Hals, their relationship remains unclear. What is known is that she successfully sued Hals for a breach of ethics after he took on one of her students.

Sofonisba was one of the first women to gain a international reputation as a painter. She studied under Campi until he moved away and this established a precedent of encouraging male painters to take on female students. Michelangelo even sent her some drawings, which she copied and sent back to him for criticism. She was a prolific painter: more than 30 signed pictures survived from her years in Cremona , with a total of about 50 works that have been securely attributed to her. Late in her life she was visited by a young painter Anthony van Dyck. A drawing of her appears in his sketchbooks, along with excerpts of the advice she gave him about painting. Nevertheless it is clear that she was an innovative portraitist, whose international stature inspired many young women to become painters.