The 22-year-old has put pen-to-paper following Saturday’s behind-closed-doors pre-season friendly against Corby Town, which the Pilgrims won 3-0.
“We have had goalkeepers training with us over a period of time,” said United boss Paul Cox, who also confirmed that a second goalkeeper will be arriving soon.
“Rhys is potentially a top class goalkeeper who could go and play at a really high level. We are pleased to get that over the line.
“We are going to bring another goalkeeper in, because I want two that are going to be really competitive with each other.
“It’s all been under control and we knew which direction we were heading in.”