2005 he made his 2nd XI debut against Derbyshire Second XI, scoring 96. In 2006 he was included in a John Paul Getty XI against the touring Sri Lankans, top scoring with 62 not out against a strong Sri Lankan side containing international bowlers. In July 2007 he scored a hundred for Harrow against Eton at Lord's. Northeast made his Kent first team debut in a List A cricket match against a touring Sri Lanka A team in July 2007, although the match was abandoned before he had the chance to bat. He went on to make his first-class cricket debut for Kent on 19 September 2007 in their final County Championship game of the season, against Durham at the St Lawrence Ground. In July 2009 Northeast showed good form for England Under 19s against Bangladesh. In the 2nd Under-19 Test match at Derby he scored 107 in the first innings and 149 in the second innings. He followed this with scores of 123, 41 and 62 in the One Day Internationals, top scoring on each occasion. In 2012 Northeast scored 880 runs at an average of 55, despite at times being relegated to the 2nd XI. He was awarded his county cap in August and was named Kent's Batsman of the Year after scoring over 1400 runs in all competitions. At the end of the season he signed a new contract for a further year. He scored his first limited over century on 20 June 2013, making 115 against the Sussex Sharks, in a world record run chase in a 40 over match. Northeast was appointed Kent's vice-captain in 2014 and acted as the on-field captain for the side throughout most of the 2015 season, including in all one-day matches. He was touted as a future captain by former Kent captain David Fulton and Darren Stevens. He scored 2,007 runs in all formats and was chosen in the Professional Cricketers' Association Team of 2015. Northeast was appointed as Kent club captain on 30 September 2015. After leading the county in first-class runs in 2016 he was selected to captain the MCC side for the 2017 Champion County match and was selected for the South team in the North v South pre-season series in the United Arab Emirates. After the end of the 2017 season Northeast's position as captain at Kent began to be questioned. The county's Cricket Committee met