Kamara was born to a Liberian mother. He attended Norcross High School in Norcross, Georgia. He played high school football for the Blue Devils football team. As a junior in 2011, he rushed for 1,300 yards with 17 touchdowns. As a senior in 2012, he rushed for 2,264 yards with 26 touchdowns, and he had 22 receptions for 286 yards and five touchdowns and led his high school to its first state championship. As a result of his successful high school career, Kamara earned Georgia Mr. Football honors from the Atlanta Journal-Constitution, named Class 6A Player of the Year, and earned first-team All-State honors from the Georgia Sports Writers Association. In addition to these accolades, Kamara was selected to participate in the 2013 Under Armour All-America Game.