Depending on how long you will have to wait for your train, you could also take the ATVO bus to Venice - Piazzale Roma and take the train from the Santa Lucia station. Much prettier wait there then at the Mestre station. I did that when flying into Venice but I did have a little wait before my train left for Udine. There is a short walk over a big bridge though if you do take the ATVO bus to Piazzale Roma. Same cost / same time on the bus to either Mestre or Piazzale Roma. Below is some info I put in my notes before I left for Italy that may be helpful.
ATVO bus info to/from airport
Marco Polo Airport to Mestre train station express bus
What to Expect
Transfer from Marco Polo Airport to Mestre Train Station with ease on the express bus service, and arrive at your destination in approximately 20 minutes.
Buses from the airport run approximately every 20 minutes from 06:06 to 00:50
The bus station is outside the Arrivals Hall at Marco Polo Airport, Exit D. Go to the second lane on the left. Buses depart from platform 1.
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At Venice Marco Polo airport, you can buy tickets in several locations:
- At the ATVO's ticket counter in the baggage-claim area.
- At ATVO ticket counters in the arrivals area (one facing the exit from baggage claim, the other to the left of the exit).
- From the ticket machines (three in baggage claim, and another three outside the terminal at the ATVO bus stops).
- From the ATVO's staff at the bus stops, who will also provide information if you need it.
**Be sure to validate your ticket before or immediately after boarding the ATVO coach. At the airport, you'll find a stamping machine on the ticket machine by the bus stop; at the Piazzale Roma, stamp your ticket in the machine behind the driver's seat unless the driver takes your ticket and punches it for you outside the bus. (You do not need to validate tickets that you ordered onlilne, since these are for specific dates.)
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Marco Polo Airport to Piazzale Roma - Venice
Buses from Marco Polo Airport are available every 20 minutes, on the hour and at 20 minutes and 40 minutes past the hour. They do not run during the night after 00:50 (01:20 from April until October). Note that the first service in the morning is at 05:20.
The airport express bus provides a non-stop service to central Venice and in just 20 minutes you’ll be dropped off at Piazzale Roma.
The bus station is outside the arrivals hall at Marco Polo Airport, exit D, 2nd lane, platform 2 on the left
The ATVO stops are located on a strip of sidewalk between two vehicle lanes outside the arrivals and baggage-claim area. Look for the No. 2 stop ("Venezia Piazzale Roma" or "Venezia Express"), which is to the left of door D as you exit the terminal.