She began acting as a teenager and came to prominence for her roles in the Disney films Stuck in the Suburbs (2004), Sky High (2005) and Read It and Weep (2006), and in the HBO miniseries Empire Falls (2005).

Panabaker came to wider attention as a cast member in the CBS legal drama series Shark (2006–2008) and is also noted as a scream queen, having starred in the psychological thriller Mr. Brooks (2007) and the horror films Friday the 13th (2009), The Crazies (2010), John Carpenter's The Ward (2010) and Piranha 3DD (2012).

After starring in recurring roles on Necessary Roughness (2011–2013), Bones (2012–2013) and Justified (2014), Panabaker guest-starred as Caitlin Snow on The CW television series Arrow in April 2014.

Starting with the series' second season, Panabaker began playing the character's alter ego Killer Frost in different capacities, in conjunction with her role as Snow, leading to subsequent guest appearances on Arrow, Supergirl and Legends of Tomorrow.

In 2006, she began her senior year at the University of California, Los Angeles, from which she graduated with a Bachelor of Arts in June 2007, again appearing on the Dean's List.

[4] In addition, Panabaker appeared in stage productions with roles in musical theater, including West Side Story, Pippin, Once upon a Time, and Beauty Lou and the Country Beast.

On May 5, 2013, Panabaker joined actors including Philip Baker Hall, Bill Pullman, and Maggie Siff in performing at Cedering Fox's WordTheatre, where they read aloud contemporary short fiction.

[19] In May and June 2019, Panabaker, DC Comics co-publisher Jim Lee, writer Tom King, and fellow CW series actresses Nafessa Williams and Candice Patton toured five U.S. military bases in Kuwait with the United Service Organizations (USO), where they visited the approximately 12,000 U.S. military personnel stationed in that country as part of DC's 80th anniversary of Batman celebration.