Coming via a statement on Thursday lunchtime, Preston publicly confirmed the approach from the Black Cats, a team they will be facing in the Championship in 2017/18, and explained that Grayson had in turn also asked for permission to speak to Sunderland.
The statement read, "Preston North End have today been contacted by Sunderland Football Club to ask permission to speak to Simon Grayson in relation to their vacant managerial position.
"Having spoken to Simon, he has asked permission to speak to the Black Cats and therefore the club had no option but to allow these conversations to take place, with a compensation package already guaranteed in his contract."
Preston coach Steve Thompson will temporarily oversee management duties at Deepdale until the subject of Grayson's future is resolved one way or another.
He steered the team to a playoff berth in his first full season in charge, with promotion back to the Championship eventually secured the following season after another playoff berth. Preston have since managed respectable 11th place finishes in back-to-back seasons in the second tier.
Grayson had previously managed at Huddersfield, Leeds and Blackpool.