I will answer your question based upon the general law as it relates to immigration consequences within the area of the 9th Circuit Court of Appeals that includes the State of Washington. I do not practice law in the State of Washington and am not familiar with the criminal laws there. I am an immigration and criminal defense attorney practicing in California. Immigration lawyers that are admitted to practice in any state and federal district court within that state and are in good standing, can practice immigration law only in any other state.
A simple DUI conviction is a misdemeanor offense. In your case, it is not entirely clear whether of not it is a misdemeanor conviction because you did not state whether you actually entered a plea. However, assuming you did enter a plea of guilty or no contest and the fact that you received a deferred sentence for 12 months and a one day jail sentence, is strong evidence that you have a misdemenor conviction under Washington state law. If you did not enter any plea at any time, then this prosecution may not have resulted in a conviction after all.
For immigration purposes, a conviction occurs at the time a plea is entered and some form of punishment is rendered by the sentencing judge. In your case, it seems as if a plea was entered and punishment was ordered by the judge of one day jail time among other conditions of probation. It does not matter that your plea may have resulted in a deferred entry of judgment of the sentence. It would be, under that scenario, a conviction for immigration purposes (assuming it is a misdemeanor and not an infraction.)
Having said that, and assuming that you entered a plea and were convicted of a simple, first time, DUI misdemeanor offense, regardless of the jail time imposed, the U.S. Supreme Court and other relevant courts have uniformly ruled that a simple DUI without any accident or driving on a suspended license enhancement(s), to the DUI, is not a crime of violence and not a crime involving moral turpitude. Accordingly, your conviction should not render you inadmissible to the U.S. However, you must disclose the fact of this conviction if asked verbally or in writing by any immigration or customs officer. A failure to do so could result in denial of your admisison to the U.S. on failure to disclose grounds.
Finally, even though your DUI conviction does not render you inadmissible to the U.S., it nevertheless, could be considered in combination with future DUI's as evidence of your being an 'habitual alcoholic' and thereby could result in you becoming deportable. The best way to handle this is to make sure that you are not convicted of any alcohol related crimes again.
The US does not deny entry to persons due to DUI convictions alone, in the instance you are citing, I believe you would be able to leave and return to the US without any immigration issue. That being said, you would need to consult an attorney in your home country to identify any issues related to entry there.
The deferred sentence will result in a dismissal of the charge (as far as the court is concerned) 12 months from the date sentence was imposed; however, be very aware that WSP and DOL will not recognize the dismissal for purposes of licensing.
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