JT Lewis was born Joseph Theodore Lewis on May 18, 2000, to Scarlett Lewis. He is the older brother of six-year-old Jesse Lewis, who was a first grade student at Sandy Hook Elementary School when he and others were killed in a shooting at the school on December 14, 2012. He was a twelve-year-old seventh grade student when his brother died. Lewis was raised on a farm with his younger brother and they had horses, dogs, and chickens, which their mother bought in 1998. Several days after the shooting, former president Barack Obama met with Lewis, his mother, and the victims' families at Newtown High School. Lewis recalled the event years later saying that "President Obama treated me with the utmost respect and class. More importantly, [he] honored my brother’s memory." Lewis attended Newtown High School and was on the varsity football team, graduating in 2018.