The 23-year-old is joining the Pilgrims on loan until January — and is likely to feature in Tuesday evening’s opening pre-season friendly against Lincoln United.
The former Leicester City trainee made his mark in senior football with Ilkeston Town before joining Mansfield Town and Grimsby Town. He also enjoyed a loan spell with Lincoln City last season.
In total, Garner has scored nine goals in 102 Conference Premier appearances.
United boss Dennis Greene told bufc.co.uk: “Signing Scott is a real coup and we have had to be patient to get our man.
“It has once again demonstrated that you have to wait for quality signings on some occasions.
“I must thank Cambridge United for their assistance in helping the move taking place.”