I worked in the US for ~9 months but now have moved back to India and do not plan to come back to the US. How do I file to get a refund on my social security payments? Thanks,

What visa did you have? If you had L1 or H1-B, then you do not get back SS tax and Medicare tax.

OPT visa. Sorry, this is for an indian colleague who moved back to India recently... I'm doing him afavor

If he had FICA (Social Security and Medicare) taxes improperly withheld from his salary while on OPT, he needs to contact his former employer to ask for a refund. If the employer refuses, he should get a refusal letter on company letterhead. The IRS requires he at least TRY to get the FICA taxes refunded in this manner.

If he unsuccessful, then he can submit Form 843 (along with a variety of support documents) to request a refund of these taxes. The refusal letter makes the processing of the Form 843 go faster, but it is NOT critical to the ultimate success of the refund request.

Form 843 is filed separately. Read: Your U.S. Tax Return: Social Security and Medicare (FICA) Taxes for Non-resident Exempt Individual