The Harlequins playmaker, more often a fly-half, will make his first start at 15 in his professional career in England’s third Pool D game, while Owen Farrell is brought back into the side at fly half after suspension.
Smith has appeared off the bench at the position in the wins of Argentina and Japan in France, but gets a first starting chance in Lille.
It was Sinfield who first broached the idea with the 24-year-old during England’s warm weather training camp in Verona in July, with Smith subsequently training regularly at the position.
And Sinfield believes that Smith’s “unbelievable skill set” should translate well to a new role, adding “variety” to England’s options for the remainder of the tournament.
“Marcus has been training at full-back with us for some time now so we’ve had a good look at him,” Sinfield explained. “He’s come on in the last two games, only for a short period against Argentina but at full-back as well.
“We feel he’s ready. He’s got an unbelievable skill set. He’s a world class player and we feel that to have someone like that in our team as a second ball player will be a great addition for us and will gives us more variety.
“We’ve got Freddie Steward there who has been great for us in the first two games, but as we move through the tournament we want to have some variety and Marcus certainly brings that.”
England are heavy favourites against Chile, who are making their World Cup debut.
The South American side managed to threaten both Japan and Samoa out wide, though, and will test a reshaped English backline.
Steve Borthwick’s side will fancy their chances of opening things up in an attacking sense, though, and Danny Care, Smith’s regular club half-back partner, is excited to see how they go.
“The kid can play anywhere,” Care, who makes his first World Cup start in eight years, said of Smith. “Whisper it quietly, he can probably play nine as well but I don’t want to get myself out of the position.
“In training he’s been brilliant whether that’s at 10 or 15. As a second ball playing option, whether it is [Owen Farrell] and George [Ford}, or George and Marcus….when they link it looks pretty special. I’m looking forward to seeing him go and can’t wait to see him light up the world stage, which I know he’s been able to do for a few years now. He’s really excited to get out there.”