He first began his career as a child, and then received recognition as a teenager for starring in the films The Seeker: The Dark Is Rising (2007) and Race to Witch Mountain (2009).

"[7] Despite his mother's early career as an actress, Ludwig had to convince his parents to support his desire to pursue acting as a child.

"[7] Ludwig studied at the University of Southern California (but left before graduating), where he was in the Phi Kappa Psi fraternity.

[3] Later he was cast in movies such as Air Bud: World Pup (2000), MXP: Most Extreme Primate (2003), Scary Godmother: The Revenge of Jimmy (2005), Eve and the Fire Horse (2005), The Sandlot: Heading Home (2007).

Ludwig's next lead role came in the part of Seth – one half of a teenage, alien brother-sister duo – in the film production of Race to Witch Mountain (2009), also starring Dwayne Johnson.

In 2014, he became a part of the main cast of the popular TV series Vikings, playing the character of Björn Ironside, the son of Ragnar Lothbrok and Lagertha.

He played the pacifist hacker Dorn in 2020's Bad Boys for Life, and also appeared in The Band Perry's music video for "Gentle on My Mind" alongside Teen Wolf actress Shelley Hennig.

[16] On August 18, 2022, it was announced that Ludwig would appear in Nicki Minaj's music video for her single Super Freaky Girl.

[18] In February 2019, Ludwig disclosed issues he experienced with depression, anxiety, alcoholism, and substance abuse starting at the age of 14.