Fennell, 20, signs from Eastern Counties League Division One South outfit Coggeshall United after making 52 appearances, scoring 33 goals in all competitions in the 2018/19 season.
Andy has featured Heybridge Swifts and was also a part of Chelmsford City youth setup with the Under 11's all the way up to the Under 18's and was a part of the Clarets reserve team.
Upon signing for City, Andy said:
"I'm really looking forward to starting with Chelmsford City.
"I've known Chelmsford for a few years. It's a good Club and I'm hoping to be able to help us get to that next level."