The 24-year-old arrives on Tyneside on a long-term contract and is manager Alan Pardew’s fifth signing of the summer transfer window.
Martinique-born Riviere joined Monaco from Toulouse in January 2013 and helped the club win the Ligue 2 title in his first few months - and scored 13 goals in 36 games for the club last season.
"I'm very happy to be here at Newcastle," Riviere told Newcastle’s 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.
"My dream was always to play in the Premier League and Newcastle have given me the opportunity to realise that."
Pardew said: "This is an important signing because the striking area is one we really had to improve.
"We have looked at Emmanuel for a while and we know he will score goals for us.
"He is quick, hungry for success and will love having 50,000 Geordies cheering him on and singing his name.
"I am really looking forward to integrating Emmanuel in the group and cannot wait to see him in action for us."
Spanish striker Ayoze Perez, former Sunderland midfielder Jack Colback, Dutch international Siem de Jong and France midfielder Remy Cabella have all arrived at St James' Park ahead of the new season.