From a young age, Glau demonstrated exceptional dedication to dance. Her perseverance earned her a scholarship to study ballet, leading to a demanding training schedule that made attending a traditional school difficult. As a result, she completed her education at home, taught primarily by her mother. In addition to classical ballet, she trained in tango and flamenco. Her early performances included roles in theatrical productions such as Le Bourgeois Gentilhomme, Peer Gynt, and Paint Your Wagon.

Glau initially aspired to become a professional dancer. Unfortunately, a serious toe injury forced her to abandon dance. With her ambitions redirected, she chose to pursue acting and moved to Los Angeles in 2002 to begin her new career path.

Acting Career Breakthrough

Summer Glau made her television debut with a guest appearance on the Joss Whedon series Angel, portraying a ballerina—a role that reflected her dance background. Her performance caught Whedon's attention, and he later cast her as River Tam in the cult science fiction series Firefly. This role became her breakthrough, earning her critical acclaim and a loyal fan following.

Following Firefly, Glau reprised her role as River Tam in the feature film continuation Serenity. She then appeared in a wide range of television shows, including Cold Case, CSI: Crime Scene Investigation, The Big Bang Theory, The Cape, Alphas, Grey's Anatomy, Hawaii Five-0, and Arrow. Her film debut, albeit in a minor role, was in the comedy Sleepover. She also featured in movies such as Help for the Holidays and Inside the Box.

In voice acting, Glau lent her voice to the character of Kara Zor-El in the animated movie Superman/Batman: Apocalypse. Additionally, she appeared in the music video for Keith Urban's "Long Hot Summer" and participated in an interactive online gaming experience.