Mackenzie, known for her roles in AMC's Halt and Catch Fire and films including The Martian and Blade Runner 2049, is in negotiations to join the film from Deadpool director Tim Miller, Variety reported.
The actress is wanted to portray a soldier on a mission as the series once again pits humans against machines, according to The Hollywood Reporter.
Former franchise star Linda Hamilton will reprise her role as Sarah Connor, the tough, action hero mother of John Connor, who goes on to lead the human resistance in the future against Skynet and its army of robots.
The film rejoins Schwarzenegger, Hamilton and Cameron for the first time since 1991's Terminator 2: Judgment Day.
The new Terminator is set to arrive in theaters on July 26, 2019 and will be a direct sequel to Judgment Day. Cameron was not involved in the handful of other Terminator films that have released since 1991, including 2003's Terminator 3: Rise of the Machines, 2009's Terminator Salvation and 2015's Terminator Genisys.