Medlen was born in Oakdale, CA, the son of John and Mary (Mimi) Medlen and brother of Eryn Medlen. He worked as a mechanic for John Force and past teammate Tony Pedregon for 8 years until Pedregon left to join his brother Cruz's race team. Medlen was moved into Pedregon's Castrol Syntec-sponsored car. In 2004, he was a top contender for the NHRA Road to the Future Funny Car Rookie of the Year. He followed with 3 wins in 2005 and 2 wins in 2006. Each year he raced, he placed in the top five or higher in NHRA Championship Points. Prior to 2004, his fastest elapsed time was 4.681 seconds. His fastest speed was 328.54 MPH. He had 8 #1 qualifiers and a 94-65 win-loss record.