I have to catch a Thalys train from Gare du Nord to Brussels at 625AM, I will be staying near Vaugrirard metro. I understand that the metro's start at 530AM. Would I have enough time even if I catch the first train and still be able to catch my 625 Thalys. This is my first trip to Paris so I dont know how long it takes to walk from Metro to Thalys terminals in Nord. Are there any other alternatives to the metro from Vaugrirard to Nord, other than a Cab? How frequent are the trains in the early mornings?

Thanks
Senthil

If you go to www.ratp.fr, you will see they recommend this route:
First, take the N62 Noctilien bus at 5:29 AM to Gare Montparnasse, and then take the Line 4 metro to Gare du Nord. I'm not sure how far it is from Vaugirard to Gare Montparnasse by walking, but it's not impossible if you are traveling lightly and start earlier.

If you fool around with the settings at that site, you may be able to figure out a bus-only itinerary.

So it looks possible, but remember that if the Thalys says departure at 6:25, it actually starts loading somewhat earlier, and it departs (in my experience) right on time. Gare Montparnasse is a huge station and it can take a while to find your metro stop. RATP says 4 minutes, but I suspect that is only true if you are walking briskly and know exactly where to go. Then Gare du Nord is not exactly tiny either.

Nord is a LOT easier to negotiate than Montparnasse IMO...frankly, if yoiu aren't familiar with the route you could do a couple of things:

DO a DRY RUN during the day so you'll know what to expect.

Spend the money for a taxi

We had to catch a train at 6:55 at Gare du Nord on a Tuesday morning. We weren't as far as you (we were in the Marais) but we still did a test run on the Monday to make sure we'd have enough time. We left at 6:00am, caught an early metro and made it with about 10 minutes to spare (metros don't run as more often that early in the morning).

Good luck!

If you took the first train from Vaugirard (5:36) and switched to line 4 at Montparnasse-Bienvenüe or walked to Montparnasse in the morning and took the earliest train you would be fine. If you go that route, I'd take Dukey's advice and do a dry run before hand at Monparnasse. I'd also make sure you have your tickets before that morning, if you don't already.

My recommended route would be to take Métro Ligne 12 (first train 5h32) to Notre-Dame des Champs, walk across the Luxembourg Gardens, and ride the RER from the Luxembourg station. You will be at Gare du Nord 10 minutes later.

No transfer at Montparnasse, then only three stops to GdN.

Thanks a lot for your replies, very informative. I will do a dry run the day before, it seems to be a very good idea.

You only need to be at Gare du Nord 20 minutes before departure as your track number won't be posted until then.

The OP won't make the train following Robespierre's suggestion. The Luxembourg gardens don't open until 7:15 am.
http://www.parisinfo.com/sites-cultu...-du-luxembourg

Walk across Rue Auguste Comte at the south end of the Gardens.