The 26-year-old makes the short trip from Gloucestershire to join the Glovers and is eligible to make his debut at Aldershot Town on Tuesday night.
Playing the majority of his career so far in League One during spells with Bristol Rovers and Northampton, Smith was part of the Cobblers side that won promotion from League Two in 2015/16.
Making 50 appearances in that campaign, the stopper was also named in the League Two Team of the Year before joining the Gas in 2017.
Appearing 28 times for Rovers last season he opted to head to the New Lawn this summer and take the number one jersey.
The commanding 6’5″ figure started out his career at Middlesbrough before joining Leicester City where he was named on the bench on nine occasions.
Experienced was also gained out on loan away from the King Power Stadium with spells at the likes of Lincoln City, Cambridge United and Mansfield.
Joining Northampton in 2015, Smith went on to make 98 appearances for the Cobblers and now arrives in Somerset due to injuries to Stuart Nelson and Liam O’Brien.