The 24-year-old is one of three fly-halves in the 31-man squad along with Colin Slade, who will wear 15 against Namibia, and legendary stand-off Dan Carter.
He has accumulated 119 points in 31 Test caps for the All Blacks, who will host the British & Irish Lions in 2017, with a win percentage of over 90 per cent.
With Carter set to step down from international duty after the World Cup, Barrett will seek to stake his claim as New Zealand's premier fly-half but he knows competition is stiff.
"Who knows if that makes us the No.1 side in the world? But we have 31 guys who could probably be starting for this team, we all have that same belief and follow the same plan, we are all on that same page.
"It was an amazing atmosphere (against Argentina). It's something you dream of just to be here. To get that first game out of the way, I am just really excited about the rest of the tournament now."
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