Smith was confirmed as Norwich head coach on Monday on a two-and-a-half-year deal, following his departure from Aston Villa earlier this month.
Cantwell was one of Norwich's standout performers in their last Premier League campaign but was frozen out under Daniel Farke, training and playing with the Under 23s. He last appeared for Norwich two months ago.
But the 23-year-old's exile is now over following Norwich's change of management, says the Daily Mail.
Smith said: "It has been a whirlwind seven days, but I'm really pleased to be back and working for Norwich.
"There's been some wonderful work at this club over the last four-and-a-half years. It is the job of myself and Craig to continue and improve on that with the aim of surviving in the Premier League."
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