Prior to pursuing an acting career, Hennig competed in beauty pageants and won the Miss Teen USA 2004 competition.

She landed her first major role as Stephanie Johnson on the soap opera Days of Our Lives (2007–2011, 2017) and went on to appear in The CW supernatural teen drama The Secret Circle (2011–2012).

She gained further prominence for portraying Malia Tate on the MTV supernatural drama series Teen Wolf (2014–2017) and CIA agent Ava Winters in the Netflix action comedy Obliterated (2023).

Three years before she won the Miss Teen USA title, one of her older brothers was killed in an accident caused by a drunk driver.

[7] Hennig also worked with a number of other nonprofit organizations, including Seeds of Peace, DARE, Sparrow Clubs, and SHiNE.

On April 20, 2007, Hennig joined the cast of Days of Our Lives in the contract role of Stephanie Johnson.

[9] In 2010, she received a nomination for the 37th Daytime Emmy Awards in the Outstanding Younger Actress in a Drama Series category.

From 2011 to 2012, she played Diana Meade, a main character in the TV series The Secret Circle, based on the books written by L. J.

[15] On March 10, 2020, Hennig was cast in an upcoming NBC comedy pilot Crazy for You in a leading role.