Dear Manish,
You have asked a question: Can potential future employers discover if I have ever been terminated from a previous company?
Answer: Your future employer could come to know about it if the employer who terminated you discloses this in the background verification (BGV). Otherwise, they would not. However, as you have been issued a relieving letter that is on par with those who had a normal separation in the company, it shows your employer's neutral mindset.
However, why were you terminated? You have not disclosed the reason. Nevertheless, the following scenarios arise:
a) Termination because of poor performance or rightsizing exercise: If the termination is due to poor performance or if the organization decides to rightsize the employee count, many mature companies consider it a normal separation. However, a few immature organizations disclose this information unnecessarily during the BGV, thereby jeopardizing the career advancement opportunities of the separated employee.
b) Termination because of a fight with the senior or fraudulent activity: Even if the termination is due to fraud, deceit, embezzlement, etc., not all organizations disclose this fraud during the BGV. They consider that termination itself is a punishment of the highest order, and there is no need to give additional punishment by blocking the career opportunities of the terminated employee by disclosing it during the BGV. A few others, in contrast, continue to disclose the actual reasons for termination and thereby demonstrate their vindictiveness.
You would know better about the organization you worked for in the past and what decision they could take.
I wish you all the best in your job search.
Thanks,
Dinesh Divekar