The 26-year-old joins the Magpies on a free transfer from the Hammers.
Newcastle manager Alan Pardew told Newcastle’s official website: “Demba made a great impression with West Ham last season and is a great signing for this club.
“He has pace, excellent technical ability, is good in the air and, it goes without saying, has the ability to consistently find the back of the net.
“Moreover he has a great passion to play for Newcastle United.”
