Janni Larsson began competing internationally in 2011, taking gold at the European trials for the World Professional Championship. After relocating to Copenhagen to study medicine at the University of Copenhagen, she trained under Shimon Mochizuki at Arte Suave (Checkmat). She won IBJJF World titles at purple belt (2012) and brown belt (2013), took double gold at the 2012 European Open, and received her black belt from Mochizuki on 17 August 2013. In 2014 she became the first Swedish black belt World Champion and was honoured by the Swedish Martial Arts Federation as Role Model of the Year. Balancing full-time work and medical studies with elite competition, she announced her retirement in April 2015 at age 28.