Smith's re-signing had been reported last week but could not be announced until Wednesday at the earliest, due to the NBA's moratorium on signings and trades.
The team did not disclose the terms of the contract, but Smith's agent, Leon Rose, said last week his client had agreed to a four-year pact worth $24.7 million.
The contract is the maximum amount the Knicks can give Smith via the early Bird rights, which allow a team to offer the average player salary with standard annual raises of 7.5 percent. The league's average salary is projected at approximately $5.5 million.
"Re-signing J.R. was one of our primary goals this offseason and we are thrilled to have him back," Knicks GM Glen Grunwald said in a statement. "He made great strides this past season with his consistent play off the bench for us, and we look forward to his continued growth."
Smith, 27, became just the third player in franchise history to win the Sixth Man Award, joining Anthony Mason and John Starks. Smith averaged a career-high 18.1 points, 5.3 rebounds and 33.5 minutes in 80 games off the bench last season.
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