Irvine, 51, was surprisingly shown the door last week despite saving the Lancashire outfit from relegation in 2007/08 and guiding them into the play-offs last season.
Kevin Russell and Scott Taylor, who were part of Ferguson's backroom staff at London Road, have also joined North End.
Preston chairman Derek Shaw insists Ferguson was the outstanding candidate for the job and backed him to embark on a successful new era at Deepdale.
Shaw said: "Darren immediately came under our radar when we began the search for a new manager and we are delighted to have him in place so quickly.
"Darren is young, British and very ambitious. We are very confident he will prove a success here at Preston North End."
Coca Cola Ch'ship Promotion 09/10 Win Outright: Preston 25/1