An amateur standout, former Team USA member and ranked No.1 by the WBA, Kenneth Sims Jr. began his boxing career at eight-years-old when his father, Kenneth Sims Sr., wanted him to learn some defensive skills. Enticed by winning, he built an extensive amateur career that saw him become a nine-time national champion and make an appearance in the 2012 Olympic Trials where he lost a one-point decision to eventual Olympian and future world champion Jose Ramirez. Sims made the decision to remain an amateur following the 2012 Olympic Trials and won the 2013 U.S. National Championships to earn a spot on the USA Boxing National Team. He was soon traveling the world with his teammates, visiting locations such as Ukraine, Ireland, Chile and Puerto Rico, culminating with an appearance in the 2013 World Championships in Kazakhstan.

Sims Jr. decided to go professional in March 2014 and quickly amassed a winning streak. With only two losses and a draw as blemishes on his record, he rebuilt himself to be one of the baddest super lightweights in the division. His breakout performance was an upset win against previously undefeated prospect Elvis Rodriguez on May 22, 2021. Sims capitalized on the moment, outboxing Rodriguez on his way to a majority decision. Since then, he has added four more victories to his resume catapulting him to the top of the rankings.

Outside the ring, Sims and his fiancé Jailyn live in the Chicago area with their daughter Nova and son Kenneth Sims III. Sims has loved every second of being a father and says that it provides a whole new motivation to be successful so he can provide for his growing family.