Nathan’s senior career started out at Havant and Waterlooville and made his first team debut in 2008 following a youth career with Portsmouth. In 2011, Nathan had a loan spell at Gosport Borough, and after some impressive performances the move was made permanent.
In his 5 years at Gosport, Nathan helped them gain successive promotions to the National League South, as well as a trip to Wembley in the FA Trophy Final. Ashmore was then snapped up by Ebbsfleet helping them gain promotion to the National League. Since then Nathan has amassed over 170 appearances for the Fleet and has won the Player of the Season award for the past two years.
In October 2019, a deal was completed between the Wood and Ebbsfleet that saw Nathan come to Meadow Park for the remainder of the 2019/20 season on a season long loan.