A friend is arriving at Gare Montparnasse around 21:30 Feb. 18 and needs to get to CDG airport for a flight leaving late the following morning. He will miss the last Air France Shuttle. Can anyone suggest the most convenient direct way? I believe one can take the Metro to St. Michel and then via Gare du Nord take another train to CDG airport but this seems rather complicated.
As @Doc mentioned, and as is mentioned on the official timetable, the last shuttle to CDG leaves Montparnasse at 22:30 (10:30 PM). If the train arrives on time, there's no issue in catching the 22:00 or 22:30 shuttle.
As it is a five minute walk from the trains to the shuttle departure, even a late train arriving before 22:15 would still allow to take the shuttle.
Alternative means of transportation include rail. From Montparnasse train station, one possibility is to take Metro line 6 to Denfert-Rochereau and then RER B to CDG. (This option will minimize walking distance inside both stations). Both lines run approximately until 00:30 (last train from Denfert-Rochereau to CDG will leave around 00:30). Time tables can be found here. Such an itinerary leaving Montparnasse at 22:30 (if last shuttle missed) can be found here.
If his flight leaves CDG late in the following morning, I would suggest to take an hotel next to the Gare Montparnasse and then take the Air France shuttle in the morning. The RER will also allow him to make it but it might be a bit less comfortable, especially if he carries a lot of luggage with him.
For whoever wanting to travel from Paris to any Paris airport, or vice versa, the Cars Air France are now Le Bus direct. Schedules can be found here:
I'm planning to use their services in 2 weeks, I've found their website very detailed and well made (e.g. to find the bus stops at the airport).