Flynn was born in Pittsburgh, Pennsylvania, USA and is the oldest of the McHugh children. His siblings Logan McHugh, Shea McHugh, Lia McHugh & Gavin McHugh are also actors. He is best known for his role as Tank in The 5th Wave.

Flynn starting acting on stage in Atlanta at the age of 7, in his most favored performance he played the role of "Jack" in Into the Woods at age 13. He spends most if his time performing for a nationally acclaimed High School show choir (2016-19).