She is best known for her roles in Stay Alive, The O.C., It's a Boy Girl Thing, and as Juliet Darling in the ABC television series Dirty Sexy Money.

Her mother designs spas for resorts and her father teaches soldiers close combat training.

Throughout 2000 to 2001, Armstrong made guest roles on television shows such as The X-Files, ER, Judging Amy and Freaks and Geeks.

She portrays the role of a self-confessed comic book reader and a sarcastic socialite from Pittsburgh who is a recurring love interest for Seth Cohen.

In 2004, Armstrong appeared on the HBO television series Entourage, as an assistant to Ari Gold and love interest for Eric Murphy.

In September 2013, she played the mother of the blond boy who perpetrated the school shooting in the Sons of Anarchy season six premiere "Straw".

Samaire has since appeared in notable small roles in films such as Would I Lie To You?, Gramercy Park and Trash.

producer McG offered the leading female protagonist role in the horror film Stay Alive.

Despite a worldwide gross of just $27,105,095 it was considered a box office success compared to the film's modest $9 million budget.

[citation needed] Armstrong starred as Nell Bedworth in the Canadian comedy It's a Boy Girl Thing, which was released on December 26, 2006, and received positive reviews from critics.

[citation needed] In 2007, Armstrong starred in a supporting role as Jenny in the horror film Rise: Blood Hunter alongside Lucy Liu.

[citation needed] Armstrong has since been cast in another independent film, a crime thriller The Last Harbor, which released in 2010.