Luggage storage Gare d Lyon

There is luggage storage in the basement of the train station - it's kind of hidden. It's only open 6:15 a.m. to 10:00 p.m. but that should work for you.
https://garedelyon.fr/guide-gare/consignes-bagages-automatiques/

There is commercial storage place on rue de Lyon right near the first metro stop from Gare de Lyon on Metro 1. I only mention this because it was right near our hotel and we passed it everyday and we often saw people using it and it's close.
https://www.citylocker.paris/en/luggage-storage-in-paris/10-bastille-gare-de-lyon-left-luggage-locker.html

Enjoy Paris,
=Tod

Thanks, hiredman. I followed your link and found an area they called "left luggage". I think that's where we would go to leave our luggage. I couldn't find any way to reserve space in advance or to find the maximum dimensions they accept but I'll keep trying. Again, many thanks.

Here is a link from SNCF detailing the locker sizes and costs at Gare de Lyon

https://www.garesetconnexions.sncf/en/stations-services/paris-gare-lyon/services-shops/lockers

Often around Europe you'll find the phrase "left luggage" which is the more British English phrase for luggage storage and when in doubt I'd search "left luggage" while in French specifically it's Consignes bagages.

According to this SNCF page: https://www.garesetconnexions.sncf/en/stations-services/paris-gare-lyon/services-shops/lockers
5.50 euros for a small locker (Height: 433 mm, Width: 347 mm, Depth: 824 mm)
7.50 euros for a medium locker (Height: 591 mm, Width: 347 mm, Depth: 824 mm)
9.50 euros for a large locker (Height: 908 mm, Width: 519 mm, Depth: 824 mm)
Lockers are rented for a fixed period of 24 hours:

The facility is very large so I doubt there are reservation concerns, but your luggage will be X-rayed so you'll probably need to interact with someone as opposed to a City Locker or private location.

As always the Man in Seat 61 provides a wealth of train and train station information:
https://www.seat61.com/stations/paris-gare-de-lyon.htm#Left_luggage_lockers
https://www.seat61.com/luggage-lockers-at-stations.htm#Left_luggage_lockers_in_Paris

Enjoy Paris!
=Tod

Oops - one more tip: When you pack in the morning think about what you'll want walking around Paris all day and specifically keep that out in your train bag separate from your luggage. That includes water, money, umbrella, warmth layer, hat, glasses, camera, sunscreen, ID, Paris tour book, charger, etc.

I know it seems obvious but when you forget that one thing then you're digging through your luggage in the left luggage area you'll think "I should have thought about this beforehand." Plan ahead and your can stash your bags, grab your day bag and walk out like to maximize your time in the city.

=Tod

Thank you so much Kim and hiredman (Tod?)! Extremely helpful information. Happy to have the website. And what a relief to hear it's a large facility. And yes, I agree that forethought is is very much preferable to hindsight. I will indeed take a previously packed day bag for the day in Paris