Is there any downside in obtaining an ITIN in order to apply for US credit card?

You might be required to file and pay U.S. taxes, but that's a question for a U.S. tax lawyer.

In general, an ITIN is only intended for people who are required to pay U.S. taxes, not for people just trying to take advantage of credit card promotions.

I don't have any specific experience with this, but here's something to consider: Unless they're just not paying attention, the bank will know it's an ITIN, and not an SSN (or EIN). This means they will know that the applicant is not eligible to work in the United States (including self employment). What they do with that information, and how it affects the overall application and/or how other information provided on the application is interpreted (such as employment and income), probably varies by bank.

That's definitely a question for a lawyer, CPA, or enrolled agent, and I'm none of those. Having said that, I'd be very surprised to find that having or not having an ITIN affects either one's obligation to pay US taxes, or obligation to file a US tax return.

It is not as easy as it used to be to get an ITIN. You now need to have a demonstrated reason for needing one and even then, they will issue it only after you file your first tax return. I have a SSN but Mr, Fink has an ITIN. We file US taxes annually and he had to renew his ITIN last year. If we had not been filing (our "reason" for needing one) they would not have renewed his ITIN.

Have a look at the site here: https://www.irs.gov/individuals/indi...ication-number

Tax return requirement: All Form W-7 applications, including renewals, must include a U.S. federal tax return unless you meet an exception to the filing requirement.

For foreigners with no US source income, having to pay taxes is based principally on residency which is a defined term. If you are resident, you pay. If not, you don't.

Credit card companies generally do not issue cards to non-resident foreigners (for obvious reasons).

So it's difficult to see how the OP can persuade the cc company to issue him or her a card, but at the same time persuade the IRS that he or she is not resident for tax purposes. To do so would involve lying on one or more occasions. This would be more than unwise as committing fraud (as it would be in lying to the cc company) could preclude all sorts of things.

The legal requirement to file and pay US taxes is independent of whether or not someone has a US SSN or ITIN.