The 32-year-old centre-back has joined the Gunners on a permanent deal for an undisclosed fee.
"David has huge experience and I look forward to working with him again," Emery told the club's official website. "He is a well-known player and adds to our defensive strength."
David Luiz is Arsenal’s sixth signing of the summer after Gabriel Martinelli, Dani Ceballos, William Saliba, Nicolas Pepe and Kieran Tierney, the latter being announced also on Transfer Deadline Day.
Arsenal start their 2019/20 Premier League season at Newcastle United on Sunday 11 August.