The versatile Spring, who can play in the back-three or the back row, helped Sligo win a Connacht Junior League and Cup double and gain promotion to the Ulster Bank League for the 2011/12 season.
He was also part of the Connacht team that won the province's first ever IRFU Junior Interprovincial Championship in May.
The 20-year-old from Sligo town is hoping to push for a place in the Shannon senior team and feature in Ulster Bank League Division 1A.
Spring, who was also a target for reigning champions Old Belvedere, told the Sligo Champion: "The opportunity to join Shannon was just too good to turn down.
"It's the spiritual home of Irish club rugby and the possibility of earning a place in the Munster Academy is another massive incentive.
"It's a huge challenge but I need to be playing at that level if I want to advance my career, so I'm really looking forward to it.
"The last few years have been pretty hectic and this summer was the first one in years that I've been able to switch off and take a break. I'm feeling very refreshed now and I just can't wait to get started with Shannon."
Spring also paid tribute to his former school and club coaches, adding: "I'm very grateful to the coaches at Sligo Rugby Club and to Jimmy Staunton and Jimmy Galvin at the Grammar School for the all the help and advice they've given me over the last few years.
"Naturally, I will miss the rugby scene in Sligo but I'm moving on to a new challenge and I'm really looking forward to it."