The 24-year-old becomes Alan Pardew's fifth signing of the summer and offers much-needed support up front after the departures of loan signings Loic Remy and Luuk de Jong and the out-of-contract Shola Ameobi.
"I'm very happy to be here at Newcastle," Riviere told the club's official website. "When the club spoke to me I said yes immediately. It was an easy decision because Newcastle is a big club with great fans and a good stadium."
The former France Under-21 international, who scored 13 goals in 36 appearances last season for Monaco, has signed a long-term deal and is looking forward to testing himself in England.
"My dream was always to play in the Premier League and Newcastle have given me the opportunity to realise that," he added.
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