Reiss Nelson was born in Elephant and Castle, London to a Zimbabwean father and English mother. He grew up in Aylesbury Estate in Walworth and attended the London Nautical School. He became friends with fellow aspiring footballer Jadon Sancho, who lived nearby, after they played together in youth tournaments.
Nelson joined the Arsenal academy when he was nine years old and made a great impression on youth coaches.
He signed his first professional contract with Arsenal on December 10, 2016, his 17th birthday.