Porsche motorsport chief Fritz Enzinger confirmed at the Night of Champions that its first Formula E driver was "already decided" and would be "announced shortly" ahead of the start of testing this spring.
Hartley managed just four points this F1 season and finished second-last in the drivers' championship. He was axed after the Abu Dhabi Grand Prix and replaced Alexander Albon.
In an interview with Newstalk ZB's Mike Hosking last week, Hartley suggested there was more to his sacking than on-track performance.
"I would love to tell the story one day," he told Mike Hosking.
"The politics I don't enjoy. It took me some time to get used to the extra media attention. What I will say is Formula One is very complicated, there's a lot of money involved, politics and some of the reasons why drivers stay or leave isn't always in your control or of reasons for pure performance.
"In any case, I left the paddock with my head held high. I knew I'd given it my best shot this year. I knew that I'd stepped up to the plate when I needed to."