Northeast was born in Ashford in Kent in 1989 and grew up in Walmer near Dover. He first came to prominence when as a 13-year-old schoolboy he scored 19 hundreds during 2003, 11 for Wellesley House School in Broadstairs, more than doubling the record for runs scored in a season for the school which had been set by Graham Cowdrey in 1977. He went on to Harrow School on a sports scholarship, winning a place in the 1st XI at the age of 14 and becoming one of the youngest players to play in the Eton v Harrow match at Lord's and the youngest for 60 years to do so. Kent County Cricket Club sent coaches to work with him at school rather than asking him to travel to Canterbury. He was part of the Harrow cricket team which was touring in Sri Lanka when the 2004 Indian Ocean tsunami struck, escaping injury by climbing on to the roof of the pavilion at Galle.