Julie Zetlin began rhythmic gymnastics instruction at the age of four. She was a member of the U.S. Junior and Senior National Rhythmic Gymnastics team from 2003-2012.
Zetlin placed 23rd all-around at the 2010 World Rhythmic Gymnastics Championships in Moscow, Russia, where she became the first U.S gymnast to advance to the world all-around finals since Mary Sanders in 2003. At the 2010 Pan American Games in Guadalajara, Mexico, Zetlin won the all-around, rope, ball, and she placed third in ribbon. In September 2011, Zetlin was named to the U.S. team for the 2011 Rhythmic World Championships, which took place during September in Montpellie, France. She was the top athlete from the continent, therefore becoming top contender for the wild-card of the 2012 Olympic Games. At the 2011 Pan-American Games in Guadalajara Zetlin captured gold medals in the all-around, ball and ribbon.
She was awarded a wild-card as the highest ranked gymnast from the Americas at the 2012 Summer Olympics in London; she placed 21st in the qualifications.