From 2009 to 2014 Lillis mainly participated in the Nor-Am Cup. He won four competitions and took second place in the overall aerials ranking in the 2010/11 season. He made his debut in the World Cup in January 2011 in Mont Gabriel and achieved 35th place. At the Junior World Championships 2012 in Chiesa in Valmalenco , he won the silver medal. In the 2012/13 season he came under the top ten twice in the World Cup and reached 17th place in the Aerials World Cup at the end of the season. At the season highlight, the Freestyle Skiing World Championships 2013 in Voss , he achieved 24th place. In the 2014/15 season he reached four top 10 placements in seven World Cup appearances and thus finished tenth in the Aerials World Cup. The FIS Freestyle World Ski Championships 2015 at Kreischberg he finished seventh.
After four results outside the top 10 places in the 2015/16 season, Lillis achieved his first World Cup podium with second place in Moscow . At the end of the season he finished seventh in Minsk and also finished the season in seventh place in the Aerials World Cup. In the 2016/17 season he achieved four top 10 placements in the World Cup and thus finished eighth in the Aerials World Cup. At the Freestyle Skiing World Championships 2017 in the Sierra Nevada he surprisingly became world champion. His best World Cup placements in the following season were two sixth places and thus achieved tenth place in the Aerials World Cup. At the season highlight, the 2018 Winter Olympics in Pyeongchang , he finished eighth. The following year he jumped at the Freestyle Skiing World Championships in Park City on the 14th place in the individual and together with Ashley Caldwell and his brother Christopher on the sixth place in the team competition.
United States
