The dancer's representative Jim Keith of the Movement Talent Agency confirmed the sad news to Entertainment Weekly on Tuesday, August 24.
"He was an amazing dancer with a huge heart and he touched the lives of everyone who met him," Keith said in a statement. "He will be truly missed. This is a sad day for us at the agency and for the dance community as a whole."
Onik's cause of death was not disclosed.
Onik competed in the 11th season of the dance show in 2014. He had most recently performed in Lin-Manuel Miranda's In the Heights, gushing of his part in June, "I mean it's for literally 2 seconds but I've never been more honored to be part of a project."
He reportedly starred in Marvel's Agent Carter, Bones, Jane the Virgin and Kirstie Alley's 100 Days of Dance web series.
Following his time on SYTYCD, he also went on to appear on Dancing with the Stars. Onik reportedly helped the U.S. Olympic figure skating team with their routines.
The entertainer was born in Ukraine before his family moved to the U.S. when he was three years old.
Fans took to social media to post tributes after learning of his passing.
"This one hurts to the core. The performing arts community is such a tight group of uber talented individuals and Serge Onik was loved and respected by so many. I'm in shock and can't find the words..." one fan tweeted.
"@sergeonik #RIPSerge a sweet, funny, very talented man. Having a hard time with this one," another fan lamented.
"I just heard the terrible news that Serge Onik passed away. I was fortunate enough to see him dance live on stage, where he was phenomenal, and he even came out to meet fans. My heart goes out to his family & friends," a third fan wrote.