Some have commented on it above, in part or comletely. But the most direct way to get from ATL to SJPdP is to:
1. Fly ATL to CDG (Paris Charles de Gaulle) - should be nonstop.
2. Drill down on this link (below) to determine the best way for YOU to get from CDG to Gare Montparnasse:
Discover how to get anywhere by searching plane, train, bus, car and ferry routes
www.rome2rio.com
3. Reserve and take a TGV from Gare Montparnasse to Bayonne. This link is my search using Wednesday 21 April as a token date:
www.sncf.com
4. From Bayonne, transfer to the TER route 62 local train to ride up into the Pyrenees. The last stop on the TER line is Saint Jean Pied de Port. Here is my search on SNCF, using the same information as above, but changing the destination from Bayonne to SJPdP:
www.sncf.com
You can clearly see that the arrival times at SJPdP are much better. Some folks find that if they travel from CDG to Bayonne - via Bordeaux, they have to overnight at Bayonne and take the first train the next morning to SJPdP. Besides, the bus ride to Gare Montparnasse gives you a nice tour of parts of Paris.
Typically, you arrive at SJPdP around dinner time. Check-in to your pre-reserved lodging. Hopefully, you planned to spend two nights there. The night of arrival and one more. I highly recommend it.
The following day - after arrival - visit the Pilgrim Office ay #39 Rue de la Citadelle, to check in, get a current conditions briefing and obtain your REALLY cool credencial and pilgrim shell. Here, they have the plain scallop shells that come from the various restaurants in town - from making Coquilles Saint Jacques.
Once you leave SJPdP, most all the shells will have come from China, and have the standard stenciled Santiago Cross on them. IMHO, the most "authentic scallop shells come from the Pilgrim Office at SJPdP.
BTW - "
Monasp" on the forum is the manager of the SJPdP Pilgrim Office at #39 Rue de la Citadelle. I believe she will answer SJPdP specific questions you might have.
Here is the Pilgrim Office web site:
https://www.aucoeurduchemin.org/?lang=en
Spend the rest of the day, obtaining last minute supplies, souvenirs, etc. Contact
Express Bourricot at:
https://www.expressbourricot.com/ Their office is next to the Pilgrim Office at #37. They can provide a number of valuable services, including:
1. Taking you to the top of the first day's climb, the first 10km head start, if you are unable to walk the rather steep climb out of SJPdP. You still have to walk about 17 km to Roncesvalles, but the worst bit on the first day is that first 8 - 10 km.
2. Moving your mochila over the mountains to Roncesvalles if you are going to use the Correos or another rucksack . mochila delivery service to move your rucksack on your Camino.
3. Taking one piece of luggage - think roll-aboard size suitcase - with your tourist clothing and things you will not need for the next month - hair dryers, shaving gear, tourist clothes, souvenirs you bought at SJPdP, directly to safe storage at Albergue / Hostal LaSalle at Santiago. If you share the space in one bag with another person, it is a bargain. Even solo, it is a very good service, reliable and secure service. I have used it several times to excellent effect.
NOTE: The mail services from France into Spain are still considered international - the EU interoperability concept has not percolated down to his service. So, try not to post anything, including a mochila, until you get into Spain. This works coming from Portugal as well.
Hope this helps.
Tom