The former Ospreys, Scarlets and Exeter Chiefs flanker left Parc y Scarlets at the end of last season and now takes over as skills and defence coach with the Whites.
Pugh replaces Ben Lewis and will work under Mefin Davies and team manager Ian Hopkins at St Helen’s.
Pugh was a part of the Wales Sevens side which won the 2009 World Cup and featured regularly on the IRB Sevens World Series.
He now returns to his first club as he takes his first steps into the coaching world.
“We are delighted to have someone of Richie’s calibre here,” said Hopkins.
“He’s recently been involved with rugby at the highest level and it’s great for him to come back to his home club.”
