Marsh, 21, spent time at the Stobart Stadium during the 2010 Championship season and returns to link up with ex-Wigan player and coach Denis Betts.
Betts said: “Stefan is an outstanding prospect. He has good vision, an outstanding turn of pace and he can certainly handle himself in the defensive department.
“Given he can play in a variety of positions across the back-line, he offers us plenty of options and will prove an extremely useful addition to the squad in our first season back in Super League.
“On behalf of the Vikings I’d personally like to thank the chairman of Wigan Warriors Ian Lenagan, plus their Head Coach Shaun Wane and Rugby General Manager Kris Radlinski, for making this deal possible.”
Marsh has played 12 times for the Warriors, scoring three tries, and made three appearances during his previous spell at Widnes, scoring a brace of tries against Toulouse.