Since making his first team debut last summer, the 20-year-old off spinner has impressed with his performances.
In 11 first-class performances to date, the pathway graduate has taken 37 wickets at an average of 25.16, including two five-wicket hauls.
During the last two domestic seasons and ahead of the latest round of LV= Insurance County Championship fixtures, only two England-qualified spinners – Matt Critchley (38 at 31.89) and Amar Virdi (42 at 28.14) – have taken more first-class wickets than the Ulsterman.
After signing his new deal, Jack said: “I’m absolutely delighted to extend my contract here at Sussex. It’s been an amazing eight years so far being involved with the county and I am looking forward to the next few years as part of this exciting young squad. I strongly believe that if the talented young players we have here continue to develop, we will bring success to Sussex in the near future.
“I’d like to thank Keith Greenfield for his help and belief in me the last few years and for Ian Salisbury’s continued expertise both as a coach and human being. He’s been an amazing help both on and off the field for me as I continue to develop. I’d also like to thank the backroom staff who have worked tirelessly with me to keep me out on the park this season and last season which has given me the platform to perform and secure my future here.”
Sussex’s Championship and One-Day Head Coach, Ian Salisbury said: “At his age and after 11 games, Jack’s record stands up against anybody’s. We see him as a major part of the future at Sussex and someone to build an attack round.
“Jack is determined not to just do well for Sussex but to step up to the highest as well. He has exactly the right mental attitude to do that. He has a very bright future in the game and fully deserves this contract extension.”
Performance Director, Keith Greenfield added: “Jack is a shining example of a young player being backed by the club and taking his opportunity to play early in first-class cricket with both hands.
“The quality he has shown already with the ball - and now bat - is exciting for the years ahead and we are delighted that he has signed a long-term extension with the club.”