Before you start

A passport valid well beyond the account opening
A work permit OR a long-stay visa (Non-B, retirement, marriage, DTV, LTR) — a few branches still open accounts for tourists, most no longer do
Often a certificate of residence (from Immigration or your embassy) or proof of a Thai address — increasingly requested
A Thai phone number for SMS one-time passwords and the mobile-banking app

Step-by-step

1
Pick a bank and a branch
Bangkok Bank, Kasikornbank (KBank) and Siam Commercial Bank (SCB) are the big, expat-friendly three. The choice of branch matters more than the bank: branches in business districts or malls (e.g. inside large shopping centres) and those used to foreigners are far more likely to say yes.
In personWho: YouSame dayFree to choose
2
Gather your supporting documents
Bring your passport plus your work permit or long-stay visa. Many branches now also ask for a certificate of residence or proof of address (a lease, or a letter from your employer or condo). Carry more than you think you need — it is easier than a second trip.
In personWho: You1–2 days to assembleResidence certificate: free (Immigration) or an embassy fee
3
Apply in person at the branch
Go to the branch, take a queue ticket, and tell the officer you want to open an account. They complete the application, take a copy of your documents, and may ask the purpose of the account. Politeness and patience go a long way if the first officer hesitates.
In personWho: You~30–60 minAccount usually free to open
4
Make the opening deposit and take the debit card
Fund the small opening deposit (commonly around 500 THB) and choose a debit card. The annual debit-card fee is typically a few hundred baht; a passbook is often issued on the spot and the card either immediately or by mail.
In personWho: YouIncluded in the visit~500 THB opening deposit + ~200–350 THB/yr debit card
5
Activate mobile banking and PromptPay
Set up the bank's app (e.g. Bualuang for Bangkok Bank, K PLUS for KBank, SCB EASY) and register PromptPay, Thailand's instant transfer system, against your account. This is what makes day-to-day life cashless. App activation needs your Thai SIM for the OTP.
Mobile appWho: You~15–30 minFree

Documents you’ll need

Passport (with current visa page and entry stamp)
Work permit OR long-stay visa (Non-B, retirement, marriage, DTV, LTR)
Certificate of residence or proof of Thai address (lease, employer/condo letter) — often required
Thai phone number (for app activation and OTPs)
Opening cash deposit (around 500 THB)

Things most newcomers don’t know

Which branch you walk into matters more than the official rules.

Thai banks give branch managers wide discretion, so requirements are applied unevenly. Newcomers routinely report being refused at one branch and approved at another the same day. If you are turned away, thank them and simply try a different branch — ideally a larger one in a business district or mall used to serving foreigners.

Source: ASEAN Now / expat-forum consensus

A work permit unlocks the smoothest path.

With a work permit (or a sponsoring employer's letter), most major banks open an account with little fuss. Without one — on a tourist or visa-exempt stamp — you are at the mercy of branch discretion, and many branches will now decline outright or demand a certificate of residence.

Source: Bangkok Bank / Expatica

Expect to be asked for a certificate of residence.

More branches now want proof you actually live in Thailand. You can get a certificate of residence from Immigration (free, but slow) or your embassy (faster, paid), or sometimes satisfy them with a lease or an employer/condo letter. Having one ready turns a maybe into a yes.

Source: Immigration / expat guides

Agents exist because the system is inconsistent.

A small industry of agents will, for a fee of several thousand baht, walk a tourist into a cooperative branch and get an account opened the same day. It is a sign of how branch-dependent the process is — useful if you lack a work permit and your own attempts keep failing, but unnecessary once you hold one.

Source: expat-forum consensus

Common mistakes to avoid

Assuming a tourist/visa-exempt stamp is enough — most branches now want a work permit or long-stay visa
Giving up after one refusal instead of trying a larger or more foreigner-friendly branch
Turning up without a certificate of residence or proof of address when the branch requires it
Not having a Thai SIM, which blocks mobile-banking and PromptPay activation
Letting the account sit dormant and unused until it gets frozen