I will be arriving around 11:30 on a weeknight and will need to get to downtown by myself, and I’m a tightwad who would add a hour transit time to save a buck 
Public transit to downtown Montreal from the airport is pah - thetic. The 204 bus is right outside the terminal (make sure you get the one whose sign says it’s going to Dorval train station). But they only run every 30 minutes or so. On weeknights there are buses at 11:28, 11:58, and 12:25, and that’s the last one of the night.
Once you get that bus, take it to Dorval train station, then locate the 211 bus stop – it’s on the bus pier that juts out from the bus terminal alongside the parking lot. There are two 211 bus stops side by side: one that says Sainte-Anne-de-Bellevue and one that says Montreal. Make sure you take the Montreal one. There are buses at 11:29, 11:49, 12:14, and 12:50 on weeknights.
This bus will take you to Lionel-Groulx metro station, on the green and orange lines. Note, though, that the last metros towards downtown leave at 12:45 a.m., and the last towards the suburbs leave at 1:06 a.m.
If you are held up and miss the last bus, do not despair. Night buses leave the terminal at 1:34, 2:34, 3:33, and 4:33 a.m.; ironically, although they pursue a very circuitous route, they actually go straight downtown from the airport, letting you off at the night bus terminus at Atwater metro station.
Tickets are $2.75 for a single fare. Remember to get a transfer on your first bus, which you can use both in the bus and the metro. (If you need to transfer to another bus after taking the metro, you must take a transfer in the station where you get on.)
The next morning when you’ve recovered, you may want to look into buying a tourist pass, either $9.00 for one day or $17.00 for three days, which gives unlimited access to the bus and metro. If you arrive on Sunday or Monday, you may want to get a CAM Hebdo or weekly pass, $19 for unlimited travel all week. Failing that, you can get strips (lisières) of 6 tickets for $11.75.
For more information, see www.stm.info or yours truly’s website at www.metrodemontreal.com .
Welcome to Montreal. Sorry about the shitty airport transit, and I hope you enjoy your stay anyway. 
matt_mcl, you’re brilliant. I’ve lived here all my life and I didn’t know this was a possibility. All I can add is, for comparison, a taxi from the airport to downtown is a fixed rate of $25, and I believe a bus shuttle to Windsor station downtown is about $15.
And Wee Bairn, definitely pay attention to those directions in bold. You could end up hours out of your way, wandering pathetically around St. Anne de Bellevue in the middle of the night, getting mugged by raccoons… 
The taxi to downtown is more like $35 these days. The bus shuttle goes to the Station centrale d’autobus at Berri-UQAM metro, but unfortunately the last one is at 11:00 p.m.
Awesome- thanks for the detailed answer. I will be printing it out and taking it with me. And may I add a follow up or two-
Are the 3 day passes available for purchase at the airport at midnight?
Also, I have to get to a friends hotel at 1005 Guy Street (Days Hotel)- can I walk that from the station?
Probably not, unfortunately. You will have to get them from a metro station downtown the next day.
To get there from Lionel-Groulx station, walk north on av. Atwater (up the hill, under the big highway) until you get to boul. René-Lévesque. Turn right, and walk about 7 blocks until you get to rue Guy (you’ll see a ridiculous-looking raised circular hotel restaurant). Turn right; the Days Inn is just below René-Lévesque.
Here’s a map: Google Maps
To get there from Atwater station if you’ve taken the night bus, walk south on av. Atwater to boul. René-Lévesque, passing the children’s hospital; turn right, and follow above directions.
So what brings you to Montreal?
I have a friend whose job has him up there for a few weeks, and he has some free time this week and asked me if I wanted to come hang out for a few days. Since I’ve never been, and since the temperature looks perfect and since France is more expensive and farther away 
, Montreal it is.
I almost forgot, all of the above reasons, plus the lure of cheese fries, which I’ve never had and am really looking forward to
The name I believe you are looking for is “poutine .” Trust me, it will cause you much less grief if you use the correct term.
And you must pronounce it poo-TINN or poo-TEEN, pronouncing the “n” as in English. Otherwise you may end up participating in an entirely different type of commercial transactiion.
Ba-dump. I’m sure Vladimir Putin would be proud.
I have just spent more time than I ever thought I would have, going over your website, matt_mcl. Very interesting!
I never really bother to look around me when I ride the metro (mostly because I don’t take it often and I’m too busy thinking “what stop are we at? How many more til I get off?” hehe). Last time I took the metro I had to get off at Square-Victoria (“Skwahr-Vict-OH-rria”) and walk up to the Beaver Hall exit… holy crap is that tunnel bizarre! And I fully agree with you that the Préfontaine kiosk is probably one of the ugliest things to have ever been created on this earth.
I’m starting up at McGill in a few weeks, but unfortunately even then I’ll just be using the Sherbrooke St. bus (we aren’t all that close to a metro stop).
Anyone notice that you can now drag the blue line showing the route, and it adapts to the streets, and you can add internediate points, and it all shows up in the directions? Impressive.
[hijack]
matt_mclThat was you on CFCF news tonight, wasn’t it? The wikipedia thing? Your name caught my ear about 5 minutes ago! You are everywhere in this city, aren’t you?[/hijack]
One error in what Matt said. You no longer get transfers. You pay your money and the machine issues a pass good for two hours that you use to get on another bus, the Metro, more buses, just so long as you don’t reverse your route. The transfer issuing machines in the Metro have been gone for months. So keep your pass. When you transfer you put your pass into a machine that reads it and returns it.
Hari, this thread is three years old; the information was accurate when I posted it.
At any rate, in that time, airport transportation has improved considerably with the introduction of the 747 airport bus, which operates 24 hours and runs directly to and from the airport terminal. It leaves from the interurban bus terminal at Berri-UQAM metro and stops at several locations in downtown along René-Lévesque as far as Guy, then at Lionel-Groulx metro; then it’s express all the way to the airport.
The 747 bus has a special fare of $7 (coins only), but the ticket is good as an all-day pass for all bus and metro routes. Other tourist, weekly, and monthly passes are also accepted on the 747 for no extra charge.
Sorry – the fare went up to $8 for the new year. That’s also the price for a one-day tourist pass, which as I mentioned the 747 ticket functions as.