Mont St Michel safe parking?

Yes and yes.

There have definitely been reports of thefts from the parking lot at MSM (as in many other tourist site parking lots in Normandy). I have never rented a car that didn't have some sort of cover or screen over the luggage compartment, but I wouldn't advertise there is anything there by rearranging your luggage in the parking lot itself. Move everything you want hidden to the storage compartment at your stop before MSM and have only your carry-ons in the passenger compartment so you can walk away from your car simply and lock it without anyone attracting any attention or anyone noticing anything left behind. And yes, Mont-Saint-Michel is usually very busy around 11:00am. As had been said many times on this forum, to get the best experience, stay overnight so you can do a lot of your visit before and after the hoards arrive by tour bus.

Ditto and ditto.
We have been to Mont St Michel six times, each time spending at least one night while leaving our rental car in the parking lot. We have never experienced, nor seen anyone else experience, any kind of car theft or other misadventure in the parking lot. Does that mean you are guaranteed to be safe? Of course not. But since you're only going to be there for a few hours in broad daylight, you (and your car, and your luggage) will likely be okay.
Follow PharmerPhil's advice and take your passports with you when you visit the island (to be extra cautious). I'm sure you'll enjoy it.

Thanks for your responses! That is reassuring. I know the island will be very busy at 11 am, but I've heard most people do not tour the Abbey. We will be there at the first week of May 2025. Thanks for your help.

Never leave things it would be a disaster to lose in a parked car. No electronics, prescription meds, ID/valuables. Carry them in a backpack. Hatchbacks are totally vulnerable and most rentals are hatchbacks. A plastic cover just advertises there is something hidden. Even if MSM parking is fairly safe, which is probably is, I would never leave the things on my list above in a parked car. stakes are too high.

Good advice! Thanks

I believe the parking lot is safe. It's fairly isolated with only people parking that are visiting the island. What time of year are you going? Usually, 11 am is busy at the Abbey. I'm not sure you can find a time that isn't, other than right before closing.

If you want to plan a fun day. I'd suggest one of the guided low tide walks in the bay. There is a TI near the gate to the city that can book you for one of these (you might need to prebook in high season). It's a bare foot activity, with your pants rolled up (wash your feet with a hose at the end). I think it would be memorable. You could time this for low tide and still make the Abbey during open hours (either before or after).

I wanted to also plan a meal at MSM but had sticker shock. I was there last in September 2016 and the cost for an omelet was over 50 euro. Pack some snacks in your car to get you through. You're probably going the other way, but Cancale isn't far away. They have the best oysters in the world. I went to a little bar/restaurant and ate on the deck with bay views. My oysters were reasonably priced, probably because it isn't touristy.

That's a long drive for one day, counting on and off highways and tourist season (dates?) traffic. MSM, via the tourist strip (alligator farms and all) is a detour.

This parking lot is vast. If you are in the more remote sections, I would be leery of leaving visible goods in the car. We managed to park close to the front, with quite a bit of foot traffic. Note that posts about Hotel parking probably means a dedicated, fenced lot unique to the hotel. But that is still not immune to break-ins.

I was once given a Euro rental contract that had "Missing luggage cover" pre-printed on the contract. Luckily, that has only happened once. Since we always take the smallest car we can manage in, it's hard to fit our luggage completely out of sight. We did, in fact, have luggage at MSM, but I don't remember if it showed or not.

Edit: Note that you are supposed to pay for parking on the way back to your car, so that you can insert/scan the paid slip at the auto exit. This is unfamiliar to some.

tagsaleaddict,
If possible, avoid meals on the island. I don't mind paying a premium for a great location or view, but MSM prices are ridiculous. We will stop for a coffee, aperitif, etc, to rest up from walking all over he mont, but eat off-island. And, to be honest, the omelets we have had there are just ordinary.

I didn't find the dinner prices that high. Of course, I didn't go for the "for tourists only" omelette on the main drag. Also, don't expect the best meal you've had in France. But you can get a decent meal with a stellar view from a few places.

Thank you for all the information! We Will be visiting the first week of May 2025.

Thanks for providing your dates. Keep in mind that both May 1st and May 8th are holidays in France. So you can expect even larger crowds at MSM and many other sites on those dates.

Thanks! Yes, I realize that.