Till was born in Fort Hood, Texas, United States, the son of Dana (née Brady) and John Till, a lieutenant colonel in the army. He has one younger brother, Nick (b. 1997). Till spent most of his childhood living in Marietta, Georgia.
Early in his life, Till’s parents became aware of his ability to imitate voices and characters. Joy Pervis discovered Till while he was attending a local acting class that his mother had enrolled him in. When he was 10, he started doing commercials as well as appearing in print. At the age of 12, he was cast in The Adventures of Ociee Nashin which he played Harry Vanderbilt, the bully of the main character. In 2004 Till played the part of Jay in the feature film Lightning Bug which filmed in Fairview, Alabama. His first major movie role was Jack Cash, the older brother of Johnny Cash who died in a sawmill accident, in the biographical movie, Walk the Line. After Walk the Line, Till was featured in a number of independent movies and films for Lifetime Television. In 2008, Till auditioned for Hannah Montana: The Movie starring Miley Cyrus and he landed the role of Travis Brody. In an interview, Till said that prior to filming he had actually never ridden a horse before. Till further stated that he does not have any current plans for another Disney movie. He attended Kell High School. After filming for The Hannah Montana Movie in Savannah, Till went back home to graduate with the Kell High School class of 2008. He worked alongside action film actor Jackie Chan in the movie, The Spy Next Door, in which Till plays the role of a Russian spy. He also starred in Taylor Swift's music video "You Belong with Me". He was in an episode of House, and on Leo Little's Big Show along with Emily Osment.
In 2008, Till starred as Jensen in Gregg Bishop's horror-comedy Dance of the Dead which was hand-picked by director Sam Raimi for distribution through Lions Gate Entertainment and Ghost House Pictures.
On July 8, 2010, it became public that he had been cast in the role of Havok in the X-Men spin-off, X-Men: First Class, directed by Matthew Vaughn. In 2013, he starred in the independent movie All Superheroes Must Die, and in 2014, he returned as Havok in the sequel X-Men: Days of Future Past. Till is set to star in the live-action/animated film Monster Trucks, directed Blue Sky Studios founder Chris Wedge, and reprised his role as Havok in the 2016 film X-Men: Apocalypse.
- During the casting of First Class, the producers told Till his audition served for both Havok and Beast, and the actor replied that despite his lifelong dream of playing a superhero, "I know you'll kill me, but if I get Beast, I'm not in the movie. I'm not going through that makeup everyday."
- He took Brazilian jiu jitsu in high school for 4 years.
- Lucas is a natural blonde but has had his hair dyed brown for the films Walk the Line and Lightning Bug.
- He likes playing a lot of video games "I'm a huge video gamer, sometimes a little too much. I'll shut myself in my room just so I can play video games all day and I end up neglecting my friends."
- Till currantary stars as Angus MacGyver on the TV series MacGyver with Vinnie Jones as a guest star.