Don't forget to buy food and drinks in advance if you need them: train stations do not always have shops, while onboard cafés are not always available and often very expensive.
With such a long journey, you could take into account travelling by plane, which is not necessarily more expensive. Doing so, you will shorten the distances and you will be able to enjoy more time in Chiang Mai.
What are the departure and arrival stations in Ayutthaya and Chiang Mai?
The trains to Chiang Mai leave Ayutthaya from Ayutthaya and arrive in Chiang Mai.
How long will it take you from Ayutthaya to Chiang Mai by train and when do the trains leave?
With the fastest connections you will be in Chiang Mai in 9 hours and 42 minutes, but on average it takes 11 hours and 29 minutes. The first train headed to Chiang Mai is at 09:10, while the last one leaves Ayutthaya at 23:10.