The 18-year-old made 36 appearances for the Tigers last season and had been on trial with Watford.
And now with a chance to impress in League Two, Smerdon is hoping to emulate some of the Grecians success stories.
“I’m delighted to have joined Exeter City," he told his new club's website. "I know about the history of the club and the players that have come through here. It’s a really good opportunity."
“There are some high-profile names to have come through like Ethan Ampadu and many others.”
Gloucester boss Mike Cook is confident the youngster can make a name for himself with his new team.
He told the club's website: "Noah had some stand out performances in the National League South so I have no doubt he will be able to make the step up into the Football League and we wish him all the best.”
Glocuester City get their 2019/20 National League North campaign underway against Blyth Spartans on August 3.
You can view a full list of Gloucester City's fixtures by clicking here.