The 33-year-old has penned a three-year contract at Kingston Park.
Botha has previous Aviva Premiership experience with Saracens, where he won the 2011 title during a five-year spell.
"I'm very excited to join the Falcons," he told the club's official website. "Newcastle are in a position to make a real impact on the Premiership this year and I am looking to help them rise up the table and push for a place in Europe.
"I want to contribute to the growing success of the club and I am also exited to learn from Dean while making the transition from player to coach eventually."
Botha made 10 appearances for England between 2011 and 2012.