The 21-year-old had denied the offence on Saracens' Nick Tompkins, which led to him being sent off during their Anglo-Welsh Cup match on Saturday.
But a disciplinary panel found him guilty, banning him until 13 December.
He will miss Newcastle's Premiership matches with Exeter, Northampton and Harlequins and the two European Challenge Cup games against Lyon.
"The tackle started off legitimately, it being a technique he is specifically coached to carry out," an RFU statement read.
"However, it did not end up as intended and having lifted the player off the ground the first point of contact between the Saracens player and the ground was the top of the shoulder."
Newcastle fly-half Craig Willis has been banned for four weeks after being found guilty of an illegal tip tackle.