I am a US citizen and my brother who is from Mexico was deported for a felony. Can I apply for a pardon for him to come back
In general, the answer is usually, but not always, no. Usually, a lawful permanent resident who is ordered removed based upon an "aggravated felony" for immigration can never lawfully immigrate, again. 'For immigration purposes,' there is no pardon/waiver for such a deportation order.
Yet, there can be a difference between a felony for state criminal purposes and an aggravated felony for deportation purposes. Also, it is unclear whether your brother may have 'derived' Citizenship as a matter of law, but the Immigration Court made a mistake.
Some attorneys claim that there are other 'arguable waiver options.' for a non-immigrant visa. This should be discussed with a 'candid' and 'experienced' immigration and visa attorney. An attorney who can take the time to discuss the situation will often charge for an appointment or teleconference. Some may eventually' become aggravated with the attorney who pursues this sort of matter.
The above is general information not meant to be legal advice. The above reply does not create an attorney client relationship.