Born in Kenya to missionary parents, Miller was primarily raised in Lancaster County, Pennsylvania.

He ran track, cross country, and played American soccer in high school.

[2] After his win of the JFK 50 Mile in 2013 with the third fastest time in course history,[3] he turned pro while continuing his cruise ship work.

[5] After his cruise work Miller was the resident caretaker at Barr Camp near Manitou Springs, Colorado for five years, which provided the opportunity to live and train at altitude on the Barr Trail and nearby Pikes Peak.

He became one of only a few American men to podium at the Ultra-Trail du Mont-Blanc 105 mile race, after coming in second to overall winner Jim Walmsley.