Deneen's father was a partner and manager of Hyak Ski Resort on Snoqualmie Pass , Washington State. The son received home schooling , so he had plenty of time to spend on sports. As a seven-year-old Deneen competed in his first alpine ski races, and in his youth he also practiced the equestrian sport of reining . At the age of 15, he finally decided to go mogul skiing. On January 15, 2005, he made his World Cup debut in Lake Placid . After a break due to injury, he won the Moguls bronze medal at the Junior World Championship in 2006.
During the 2006/07 season, Deneen competed in races in the Nor-Am Cup. With good performances in this continental championship, he secured a starting place in the World Cup again. On January 18, 2008, he got his first World Cup points when he was third in Lake Placid; he repeated this result two days later in the same place. In the course of the 2007/08 season he established five more top 10 placements (including another third place) at the top of the world. This earned him the Rookie of the Year award .
Deneen's performances in the 2008/09 season were highly inconsistent and ranged from 3rd to 47th place. At the 2009 World Cup in Inawashiro . In the Moguls competition he succeeded for the first time in showing the new jump Back X - a backflip with crossed skis - in both runs without mistakes . With this he secured the world championship title with a large point advantage. At the beginning of the 2009/10 season , inconsistent performances followed. With a victory in the US eliminations, however, he secured qualification for the 2010 Winter Olympics . At the Olympic competition in Cypress Mountain , he fell and was classified in 19th place. In the World Cup, two podiums followed in Åre .
On December 11, 2010, Deneen won a moguls competition in the World Cup for the first time in Ruka . In the 2011/12 season, three more victories followed, which resulted in second place in both the overall and the discipline rankings. In the winter of 2012/13 Deneen achieved six podium finishes, and at the 2013 World Championships in Voss , he won the bronze medal in both disciplines. In the winter of 2013/14 he achieved three World Cup podiums.