She is known for her starring roles as Max Black in the CBS sitcom 2 Broke Girls (2011–2017) and as Darcy Lewis in the Marvel Cinematic Universe (MCU) superhero film and television franchise beginning with Thor (2011).

[1] She graduated from high school early at age 14,[12] and moved with her family to Los Angeles to pursue acting full time.

[3] In an interview with Philadelphia magazine in 2008, she explained that she chose "Dennings" as her professional surname because she thought her family name was "a little hideous" and she "wanted to know when someone really knew [her] or they didn't.

In February 2004, she was cast in a pilot for CBS titled Sudbury, about a family of modern-day witches, based on the 1998 film Practical Magic, but the series was not picked up.

Dennings made her feature film debut in Hilary Duff's Raise Your Voice in 2004 as Sloane, a somber piano student.

[12] In 2006, Dennings played a rebellious teenager in the crime comedy film Big Momma's House 2, starring Martin Lawrence.

[18] Dennings starred in Charlie Bartlett in 2008, the story of a wealthy teenager (Anton Yelchin) who acts as a psychiatrist among students at his new public high school.

Actors Sam Rockwell and Josh Hartnett were also involved, but the project was not greenlit because of its subject matter of nuclear war was considered too controversial.

[24] Dennings and other rising stars were featured in the August 2009 issue of Vanity Fair, photographed re-enacting scenes from famous Depression-era films.

[28][29] The following year, she starred in the independent feature Daydream Nation, as a girl who moves from the city to a strange rural town, and is caught in a love triangle with her high school teacher (Josh Lucas) and a teenage drug dealer (Reece Thompson).

[31] In May 2010, Dennings appeared in a music video for "40 Dogs (Like Romeo and Juliet)", a single by Austin, Texas-based musician Bob Schneider.

[30] In February 2011, Dennings was cast in 2 Broke Girls, a CBS sitcom written and produced by Michael Patrick King and comedian Whitney Cummings.

Beth Behrs co-stars as a Manhattan heiress who lost her inheritance, while Dennings plays a tough outspoken girl from Brooklyn.

[37] Dennings starred in the drama film To Write Love on Her Arms (originally titled Renee) in 2012, with Chad Michael Murray and Rupert Friend.

She played Renee Yohe, a Florida teenager who struggled with substance abuse and self-injury, and who inspired the founding of the nonprofit organization To Write Love on Her Arms.