Launchbury, who initially only linked up with the squad on Monday as injury cover for Tom Palmer, has been preferred to Saracens lock Mouritz Botha and Harlequins' George Robson.
Vunipola's inclusion as one of four props in England's match-day squad was well sign-posted after an impressive start to the Aviva Premiership season with Saracens.
England head coach Stuart Lancaster will confirm his starting XV and eight-man bench for the Fiji clash on Thursday morning.
Meanwhile, Scarlets prop Deacon Manu has been confirmed as captain of Fiji.
The 33-year-old, who has 12 caps to his name, led Fiji on their 2010 tour of Europe and in last year's Rugby World Cup.
"Manu has led the team before and has shown good leadership skills," said Fiji coach Inkike Male.
"With his experience and the respect the boys have in him, I am confident that he has the qualities in him to not only lead the front row, but the whole team."
England's 23-man squad for Saturday's QBE autumn international against Fiji at Twickenham (kick-off 2.30pm):
Forwards: D Cole (Leicester Tigers), T Johnson (Exeter Chiefs), J Launchbury (London Wasps), J Marler (Harlequins), T Palmer (London Wasps), D Paice (London Irish), G Parling (Leicester Tigers), C Robshaw (Harlequins, capt), M Vunipola (Saracens), T Waldrom (Leicester Tigers), D Wilson (Bath Rugby), T Wood (Northampton Saints), T Youngs (Leicester Tigers)
Backs: B Barritt (Saracens), M Brown (Harlequins), D Care (Harlequins), O Farrell (Saracens), T Flood (Leicester Tigers), A Goode (Saracens), U Monye (Harlequins), C Sharples (Gloucester Rugby), M Tuilagi (Leicester Tigers), B Youngs (Leicester Tigers).