The 21-year-old Wales Under-21 skipper arrives at Huish Park on a three-month loan deal and goes straight into Skiverton's squad for Saturday's home clash against Brentford.
Skiverton said: "We are delighted to get Shaun in on loan. Our patience has paid off.
"He is one we have coveted from afar this season and as soon as the opportunity presented itself to get him here we have acted."
Meanwhile, MacDonald himself hopes playing a starring role for the Glovers can help reignite his career with hometown club Swansea, but that is not the first thing currently on his mind.
He told the South Wales Evening Post: "My contract runs out next year but I am not going to worry about contracts for the moment. I think everybody knows that my dream is to play for Swansea, my hometown team. But I am not getting games at the moment and I just want to play."