Jacobellis had her first international success at the Snowboard Junior World Championships in 2002 in Rovaniemi . She won the gold medal in snowboard cross. The following year she won the gold medal in the halfpipe at the Junior World Championships in Prato Nevoso . She completed her first World Cup at the beginning of the 2003/04 season in Valle Nevado and finished second in the halfpipe. In the further course of the season she won four world cup victories in Joetsu-kokusai and on Mount Bachelor and thus achieved ninth place in the halfpipe world cup, third place in the snowboard cross world cup and second place in the overall world cup.
After her fifth World Cup victory at the beginning of the 2004/05 season in Valle Nevado, Jacobellis won the halfpipe at the US Snowboarding Grand Prix on Mount Bachelor and in Mountain Creek . At the season highlight, the Snowboard World Championships 2005 in Whistler , she won gold medal in snowboard cross. She was also eighth in the halfpipe. At the end of the season she won the snowboard cross at the World Cup in Lake Placid and reached fifth place in the snowboard cross world cup. At the beginning of the following season, she won snowboard cross in Valle Nevado. At the following World Cup in Saas-Fee , she came second in the halfpipe and third in snowboard cross. At the 2006 Winter Olympics , she awarded the gold medal in the snowboard cross competition. Since she had a big lead over the other riders in the final run, she tried a “grab” on the last jump, but fell on the snowboard with this grip. The Swiss Tanja Frieden managed to overtake her and Jacobellis remained the silver medal.
In March 2006 Jacobellis was second in snowboard cross at the World Cup in Furano and reached 11th place in the overall world cup and sixth place in the snowboard cross world cup. After finishing third in the halfpipe at the US Snowboarding Grand Prix in Breckenridge , she was again world champion in snowboard cross in Arosa . In February 2007 she took second place in the half pipe at the US Snowboarding Grand Prix in Tamarack and in snowboard cross at the World Cup in Furano. The following month she won two world cup victories in snowboard cross in Lake Placid and thus won the snowboard cross world cup. In the overall World Cup she achieved 12th place. At the beginning of the 2007/08 season she finished second in the halfpipe in Cardrona and won again in snowboard cross in Valle Nevado. In the further course of the season she won three world cup races. She also took second place in snowboard cross and third place in the halfpipe at the World Cup in Sungwoo . She finished the season in second place in the overall world cup and in the snowboard cross world cup.
Since the 2008/09 season Jacobellis has only started in the snowboard cross discipline. In the 2008/09 season she won five World Cups and took third place once. At the end of the season she won the Snowboard Cross World Cup and, like last year, came second in the overall World Cup. In the following season she was in the top ten five times in the World Cup. She won in Bad Gastein and Chiesa in Valmalenco and at the end of the season reached 12th place in the overall World Cup and fourth place in the Snowboard Cross World Cup. At the season highlight, the 2010 Winter Olympics in Vancouver , she was fifth. After finishing fifth at the World Cup in Telluride at the beginning of the 2010/11 season , she won the gold medal at the 2011 Snowboard World Championships in La Molina . Two World Cup victories and a second place in Arosa followed. She finished the season in third place in the Snowboard Cross World Cup.
In the following season Jacobellis won all three competitions in the World Cup and thus finished fifth in the Snowboard Cross World Cup. After taking a break in the 2012/13 season , she won twice third and once second place in the 2013/14 World Cup. In Lake Louise she won her 27th World Cup and at the end of the season she finished second in the Snowboard Cross World Cup. She finished seventh at the 2014 Winter Olympics in Sochi . In the following season she achieved tenth place in the snowboard cross world cup with places 11 and three. In January 2015 she became world champion for the fourth time at Kreischberg . In the 2015/16 season , she was among the top seven in all World Cup competitions. She took second place twice and thus reached sixth place in the Snowboard Cross World Cup.
In the 2016/17 season, Jacobellis took third place in the World Cup twice and came second once, thus reaching fifth place in the Snowboard Cross World Cup. In addition, she won the team competition in Solitude together with Rosina Mancari . At the season highlight of the Snowboard World Championships 2017 in Sierra Nevada , she won the bronze medal together with Faye Gulini in the team competition and the gold medal in the individual. In the 2017/18 season she took two wins and finished second once, reaching sixth place in the Snowboard Cross World Cup. At the season highlight, the 2018 Winter Olympics in Pyeongchang , she came fourth in snowboard cross. In the 2018/19 season she won in Cervinia and Feldberg. In addition, she took second and third place once and at the end of the season, second place in the Snowboard Cross World Cup. At the Snowboard World Championships 2019 in Park City , she finished fifth and won the gold medal in the team competition.
At the Winter X Games she has won 11 medals so far, nine of them gold. (As of March 2016)