He is currently in the Scotland warm-up squad for the up-and-coming World Cup in Japan.
Speaking of his return to Millbrae, Reid said: "It is great to be back where it all started for me. Ayr is my home and it allows me to be close to my family.
"Obviously it is always a massive honour to wear the thistle and I would relish the chance to play at another world cup, so I've just got to put in the graft and whatever comes, comes."
Reid joins Frazier Climo as the Bulls' second signing, after it was revealed last month the New Zealander would ply his trade as both a player and skills coach for the Bulls.
Head coach Peter Murchie has expressed his positivity on having Reid onboard and how his squad is coming together: "He is a player who brings experience from the top-end of the game and the fact he is in the current world cup squad shows he's still firing from all cylinders. He is an Ayr boy who is loved here, so it's great for fans to see him come back ahead of the maiden Super6 season.
"The rest of the squad is piecing together nicely. We are in a good place with recruitment and over the next four to six weeks we will be able to start naming some of the talents we have.
"I'm excited about the challenge that lies ahead this season."
The Ayrshire Bulls will play in the Super6 league, with Ayr RFC competing in the National Leagues. Ayr Rugby has always represented players from all over the south-west coast of Scotland and a name change to Ayrshire reflects this. The name also gives a nod to the rich history of Bull farming in the area.