For obvious reasons, U.S. law is set up to protect the country against foreign visitors who commit crimes here. Among the various crimes that can make a non-citizen of the United States deportable are so-called aggravated felonies. Thus a foreign-born person who is in the United States with a visa or a green card (lawful permanent residence) and who commits an aggravated felony can be removed or deported from the country. Figuring out which crimes are aggravated felonies is, however, not always easy.
You can't judge a crime by its name. People who have been convicted of ordinarily low-level crimes categorized as misdemeanors, or of other crimes that were not charged as felonies in their state, have been found to have committed an aggravated felony and then deported.
In immigration law, aggravated felony is defined far more broadly than in most state's criminal laws. The definition is found in Section 101(a)(43) of the Immigration and Nationality Act, or Section 1101(a)(43) of the U.S. Code. In summary, the federal law definition names the following as aggravated felonies:
(A) murder, rape, or sexual abuse of a minor
(B) illicit trafficking in a controlled substance
(C) illicit trafficking in firearms or destructive devices or in explosive materials
(D) money laundering or engaging in monetary transactions in property derived from specific unlawful activity if the amount of the funds exceeded $10,000
(E) certain explosive materials or firearms offenses
(F) a crime of violence (not including a purely political offense) for which the term of imprisonment at least one year
(G) theft (including receipt of stolen property) or burglary if the term of imprisonment was at least one year
(H) kidnapping or making a demand for or receipt of ransom
(I) child pornography
(J) racketeering, or gambling if a sentence of one year imprisonment or more could have been imposed
(K) owning, controlling, managing, or supervising a prostitution business; transportation for the purpose of prostitution if committed for commercial advantage; or peonage, slavery, involuntary servitude, or trafficking in persons
(L) gathering or transmitting national defense information, disclosure of classified information, sabotage, treason, or compromising the identity of undercover intelligence agents
(M) fraud or deceit in which the loss to the victim or victims exceeds $10,000; or tax evasion in which the revenue loss to the Government exceeds $10,000
(N) alien smuggling, except a first offense for which the alien has affirmatively shown the purpose of assisting, abetting, or aiding only the alien's spouse, child, or parent (and no other person)
(O) illegal U.S. entry by an alien who was previously deported on the basis of an aggravated felony conviction
(P) falsely making, forging, counterfeiting, mutilating, or altering a passport or instrument (document fraud) for which the term of imprisonment is at least 12 months; except in the case of a first offense for which the alien has affirmatively shown that the offense was committed for the purpose of assisting, abetting, or aiding the alien's spouse, child, or parent (and no other person)
(Q) failure to appear for service of sentence if the underlying offense is punishable by imprisonment for five years or more
(R) commercial bribery, counterfeiting, forgery, or trafficking in vehicles the identification numbers of which have been altered, if the term of imprisonment is at least one year;
(S) obstruction of justice, perjury or subornation of perjury, or bribery of a witness, for which the term of imprisonment is at least one year
(T) failure to appear before a court pursuant to a court order to answer to or dispose of a charge of a felony for which a sentence of two years' imprisonment or more may be imposed
(U) an attempt or conspiracy to commit an aggravated felony.
The best thing to do if you've been charged with a crime, and you are not a U.S. citizen, is to hire not only a criminal lawyer, but an immigration lawyer. The immigration lawyer can help make sure that the crime with which you're charged or to which you agree to plead guilty is not likely to be defined as an aggravated felony under the immigration laws.
If you are low income, the government should provide you with a free criminal lawyer (a "public defender"). However, you will need to separately pay for the immigration lawyer. It's probably worth the cost, because few criminal lawyers understand the implications of criminal convictions in immigration cases. The criminal lawyer might give you advice that would be good for a U.S. citizen; for example, "Plead guilty to this and you'll avoid jail time!"; but that might be the worst advice from an immigration standpoint, and result in your deportation.
And if you have already been convicted of a crime, and are facing removal, you'll also want to hire an immigration attorney, if possible. If you're not yet a permanent resident, but are only in the U.S. on a nonimmigrant visa, you can be removed from the U.S. without a hearing before a judge in immigration court.
As an apparent aggravated felon, expect to be placed in detention. Aggravated felons are not eligible for release on bond.
Aggravated felons are not eligible to apply for asylum or the protections of the Convention Against Torture, despite any fear they might have of persecution in their home country. They are also not eligible for a defense to removal known as cancellation of removal.
Once you've been convicted of an aggravated felony and removed from the U.S., you are permanently inadmissible. In other words, you will never again be eligible for a U.S. visa or green card.