Ferris, the only current Ulster player named in Ian McGeechan's 37-man squad, was one of the key components in an Irish forward pack that secured a first Grand Slam in 61 years earlier this season and Williams is certain his inclusion is just reward for a fantastic year at both domestic and international level.
"It's deserved. Stephen has been great all year," said Williams.
"He has had a bit of injury but since he has got back to back games in November and especially since Christmas he has been fantastic."
With only 13 Test caps to his name and having only cemented his place in the Ireland starting XV this season, Ferris is by far the least experienced flanker in the touring party.
Despite his relative lack of experience, Williams believes the tour will be great for his player and the player himself will be great for the tour.
"I've said to him you've got to take the tour very much as a learning curve," added Williams.
"It's six weeks and back-to-back games which really a lot of the modern players don't do.
"Stephen has got to go in and grow with the tour and soak it all up and learn what he can from the other players.
"He is such a powerful guy, he's competitive and such a decent bloke that he'll fit into the tour spirit."