Wash and dry the potatoes. Scrub the skins well, then dry them thoroughly with kitchen paper. Removing as much surface moisture as possible helps give you a better skin.
Pierce the potatoes. Pierce each potato several times with a fork so steam can escape while they cook.
Season the potatoes. Rub the potatoes all over with the olive oil, then season with salt and black pepper.
Wrap in foil. Wrap each potato individually in foil. I put the thicker folded section of foil underneath when placing them into the slow cooker.
Slow cook. Arrange the potatoes in the slow cooker and cook for 5 hours on HIGH or 8 hours on LOW.
Check they are cooked. Push a sharp knife or skewer into the centre. It should slide through easily with very little resistance.
Notes
The timings have been tested using large baking potatoes weighing approximately 350g each. We cooked them in a 4.5L slow cooker.
Potato size makes a difference. Check smaller potatoes sooner and allow extra time for particularly large ones.
You do not need to add any water to the slow cooker.
Try to use similarly sized potatoes so they cook evenly.
For softer, evenly cooked skins, wrap the potatoes in foil as directed.
For a slightly drier and browner skin, cook without individual foil and place the potatoes on baking paper instead.
Slow cooker jacket potatoes won't naturally have the same crispy skin as oven-baked potatoes. For extra crispiness, finish them briefly in an air fryer or hot oven.
Check doneness with a knife or skewer rather than relying only on the clock.
Don't assume the potatoes cannot overcook. Smaller potatoes or hotter slow cookers may be ready sooner.
For the best texture, serve the potatoes soon after they finish cooking.