Gare Du Nord to Montparnasse by Metro

There is no RER service of commuter style trains between the Gare Nu Nord, where the Eurostar will arrive, and the Gare Montparnasse on the other side of the city centre; which is where the trains on to western France will be departing from.
So if you don’t want to take a taxi, then the Metro is the fastest public transport option - though bus Line 91 also goes to Montparnasse from the Gare Du Nord, it leaves from the stop on Rue de Saint-Quentin

Taking the Metro looks straightforward, as Metro Line 4 provides a direct link between Gare Du Nord and Montparnasse (direction Mairie de Montrouge).
It’s also at least 5 x cheaper than taking a taxi and almost certainly faster too, despite it being a 14 stop journey; you will be on the Metro train for around 20 minutes.

The total transfer time, from stepping off the Eurostar at the Gare Du Nord to being on the concourse at Montparnasse will be 35 - 40 minutes, as the transfer from Metro to main line departures at Montparnasse will take around 15min.
However, the queues at the ticket machine can add another 10 to 15mins, so it's best to allow at least an hour to make the transfer from Nord to Montparnasse.

The four stages for making the transfer to metro line 4 at Gare Du Nord from Eurostar and Thalys train arrivals:

Walk ahead to the front of the train and exit on to the main concourse, which is the only exit from the platform/voies.

There are two routes to Metro Line 4.

The easiest option is to turn left when you exit from the voie (platform/track) and keep walking ahead until you are at the far side of the concourse - keeping the trains to your left.
In this part of the station you will come to an escalator that leads to a lower concourse.
The image above left has been taken from the top of this escalato - when you step off of the escalator, initially walk ahead of you, but then turn sharp right, the Line 4 entrance will then be ahead of you.

Alternatively there is the most obvious option, which is to use one of the access points to the Metro which are located opposite the exits from the voies (platforms/tracks) in Hall 1 - one of which is pictured above

Your end-2-end train journey ticket will not include the Metro, so you will need to buy the Metro-Train-RER ticket, which costs €2.50.

Worth knowing is that Paris has pretty much transitioned to a Pay As You Go system for its public transport network, based on navigo cards.
There are two core methods of using navigo:
1 - A plastic card which is automatically issued by ticket machines and ticket counters when you inform the machines or staff, that you don't already have a card - the cost of the card is €2.
2. Downloading the navigo app to a mobile device.

The big plus of bothering to download the mobile app, is that you can then use mobile banking to pay for tickets to be added to it, so can then avoid the ticket machines and counters!

The staffed ticket counter in the Metro station is only open at certain times of the day, so queues of more than 10 people per ticket machine can be typical.

The excellent parisbytrain website has all the info you will need about metro tickets.

Make your way to the platform for the Line 4 trains heading to Mairie de Montrouge - taking the staircase down is the only option!

Before opting to take the Metro from Paris Nord to Paris Montparnasse, these six things are worth considering:

1. Gare Du Nord is the busiest Paris Metro station and Line 4 is its 2nd busiest line, so at peak times the crowds can seem overwhelming.
   You may not be able to even board the first train to arrive.

(2) The access to the Line 4 Metro platform at Gare Du Nord is NOT step free.

(3) There are no luggage spaces/racks on the trains and they’re not air conditioned either, so they can be uncomfortably hot!

(4) You will leave the train at Montparnasse – Bienvenüe station, look out for the stop after St-Placide.

(5) The part ofMontparnasse – Bienvenüe metro station that the Line 4 ues is connected to Paris Montparnasse station by long passage ways.
So long that despite the provision of a travellator, it takes around 12 -15 minutes to from stepping off the Metro being on the main concourse at Montparnasse (a long way to run if you're in a hurry!)

You will first have to negotiate three short flights of stairs to access the travellator.
And the travellator itself is long!

(6) When you finally exit the metro station, the mainline trains will be two levels above you, though there are banks of escalators and lifts/elevators.

Bus line/route 91 is now the core inter-station bus service in central Paris.
One end of its route commences at the Gare Du Nord, from the stop on Rue de Saint-Quentin and it arrives in the small bus station in front of Gare Montparnasse.

As the line 4 route is less than ideal for those with heavy luggage and small children etc, on a recent visit to Paris I checked out what should be the quickest, indirect alternative route.
I took an RER line B train to Denfert-Rochereau station and connected there for Metro line 6, because at Montaparnasse, the line 6 stops much closer to the exit from the Metro station.
However, neither the transfer at Denfert-Rochereau or the exit from Line 6 at Montparnasse is step-free, so the route isn't any easier than taking line 4 direct - and the concourse to concourse journey time is similar too.

If you will be taking a TGV from Paris Montparnasse - from the Metro, follow the signs to ‘Lignes Grande Vitesse’.
The first level above street level isn't where the TGVs depart from. you will need to go up another level into Departure Hall 1, pictured below.

If your train hasn't arrived in the Gare Du Nord exceptionally late, you won’t be able to automatically swap train departure specific tickets to a subsequent departure from Montparnasse, IF you miss your booked connection due to a delay on the Metro, OR because your taxi got stuck in traffic.
So look carefully at the combination of trains that can be offered by ticket agents, our preference is to allow a minimum of 75 mins between the arrival time of a train at Gare Du Nord and the departure of a train from Gare Montparnasse.

1: The Silver Segway Tour is a mini-group tour so is ideal for a family or a group of friends.
A guide will help you to take unforgettable photos along the route, which includes the Eiffel Tower – Field of Mars – The National Residence of the Invalids – The Pont Alexandre III – Museum of the Civilisation.

2: The "Paris And Versailles" trip is a guided explorer tour that includes accommodation, transport and others and takes 5 days.
With the In-depth Cultural tour Paris and Versailles, you'll have a 5 days tour package taking you through Paris, France and Versailles.

3: The Montmartre by Night tour of Paris in Citroen 2CV is the Paris excursion with a difference!
You’ll begin your Montmartre by Night tour of Paris with a drive along the Avenue des Champs Elysées to the Arc de Triomphe, before passing by splendidly illuminated monuments such as the Eiffel Tower, Invalides, Louvre and Notre Dame Cathedral.
Your magical night time Paris excursion continues as you wend your way through Montmartre as you take in some of Paris’s best-known nightlife, including the Moulin Rouge and Pigalle district and then culminates at the Sacré Coeur basilica
And to make sure that you enjoy a truly sparkling experience, this Paris excursion comes complete with a complimentary bottle of champagne!

4 This Champagne from Paris day tour will allow you to get acquainted with the region of Champagne, and try the most famous and wonderful drink which reflects the main traditions of France.
Get to see three different Champagne producers, taste seven different types of champagne and enjoy an exquisite 4-course lunch at a vineyard.