Ludwig was born in Vancouver, British Columbia. He has three younger siblings: a sister and brother named Nicholas, who are twins, and a younger sister. His mother, Sharlene (née Martin), is a former actress, and his father, Harald Horst Ludwig, is a businessman and the co-chairman of the board for Lions Gate Entertainment Corp. Ludwig was drawn to the profession, saying in an interview: "I have a big imagination. I love performing." Yet, despite his mother's early career as an actress, Ludwig had to convince his parents to support his desire to pursue a career as a child actor. His parents believed that child actors "can get sucked into a life that isn't reality." Ludwig is enrolled as a theatre major at the University of Southern California where he is in the Phi Kappa Psi fraternity, and lives full-time in Los Angeles.
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, the wrestler-turned-actor. Seth is the part originated by Ike Eisenmann in the 1975 original, Escape to Witch Mountain. The film opened at number one at the box office the weekend that it premiered, with receipts estimated at $25 million. Despite his early casting success with The Seeker, Ludwig indicated in an interview that it was his intention to attend university. In another interview, the actor said that the most challenging thing about filming The Seeker was trying "to juggle school while filming." He stated: "My school wasn't used to it, and I wasn't used to it. It was the most amazing experience, but it was really hard."