Diallo was born in Queens, New York in 1998. He is the son of Marima and Abdoulaye Diallo and has three siblings. For his first two years of high school, he played at John Browne HS in Flushing, New York. After garnering attention at the 2015 Under Armour Association Circuit and the NBPA Top 100 and Adidas Nations camps, Diallo transferred to Putnam Science Academy in Putnam, Connecticut before his junior season. He was heavily recruited by six universities and ultimately choose Kentucky. During his rookie NBA season, he hosted Hami Diallo's Community Day in Flushing, giving back to his community with a "day full of giveaways, basketball games and music". You can follow Diallo on Twitter (@hamidoudiallo) and Instagram (@hami.diallo).