Petitioner Jae Lee moved to the United States from South Korea with his parents when he was 13. In the 35 years he has spent in this country, he has never returned to South Korea, nor has he become a U. S. citizen, living instead as a lawful permanent resident. In 2008, federal officials received a tip from a confidential informant that Lee had sold the informant ecstasy and marijuana. After obtaining a warrant, the officials searched Lee's house, where they found drugs, cash, and a loaded rifle. Lee admitted that the drugs were his, and a grand jury indicted him on one count of possessing ecstasy with intent to distribute. Lee retained counsel and entered into plea discussions with the Government. During the plea process, Lee repeatedly asked his attorney whether he would face deportation; his attorney assured him that he would not be deported as a result of pleading guilty. Based on that assurance, Lee accepted a plea and was sentenced to a year and a day in prison. Lee had in fact pleaded guilty to an "aggravated felony" under the Immigration and Nationality Act, 8 U. S. C. §1101(a)(43)(B), so he was, contrary to his attorney's advice, subject to mandatory deportation as a result of that plea. See §1227(a)(2)(A)(iii). When Lee learned of this consequence, he filed a motion to vacate his conviction and sentence, arguing that his attorney had provided constitutionally ineffective assistance. At an evidentiary hearing, both Lee and his plea-stage counsel testified that "deportation was the determinative issue" to Lee in deciding whether to accept a plea, and Lee's counsel acknowledged that although Lee's defense to the charge was weak, if he had known Lee would be deported upon pleading guilty, he would have advised him to go to trial. A Magistrate Judge recommended that Lee's plea be set aside and his conviction vacated. The District Court, however, denied relief, and the Sixth Circuit affirmed. Applying the two-part test for ineffective assistance claims from Strickland v. Washington, 466 U. S. 668, the Sixth Circuit concluded that, while the Government conceded that Lee's counsel had performed deficiently, Lee could not show that he was prejudiced by his attorney's erroneous advice.

Held: Lee has demonstrated that he was prejudiced by his counsel's erroneous advice. Pp. 5-13.

     (a) When a defendant claims that his counsel's deficient performance deprived him of a trial by causing him to accept a plea, the defendant can show prejudice by demonstrating a "reasonable probability that, but for counsel's errors, he would not have pleaded guilty and would have insisted on going to trial." Hill v. Lockhart, 474 U. S. 52, 59.

     Lee contends that he can make this showing because he never would have accepted a guilty plea had he known the result would be deportation. The Government contends that Lee cannot show prejudice from accepting a plea where his only hope at trial was that something unexpected and unpredictable might occur that would lead to acquittal. Pp. 5-8.

     (b) The Government makes two errors in urging the adoption of a per se rule that a defendant with no viable defense cannot show prejudice from the denial of his right to trial. First, it forgets that categorical rules are ill suited to an inquiry that demands a "case-by-case examination" of the "totality of the evidence." Williams v. Taylor, 529 U. S. 362, 391 (internal quotation marks omitted); Strickland, 466 U. S., at 695. More fundamentally, it overlooks that the Hill v. Lockhart inquiry focuses on a defendant's decisionmaking, which may not turn solely on the likelihood of conviction after trial.

     The decision whether to plead guilty also involves assessing the respective consequences of a conviction after trial and by plea. See INS v. St. Cyr, 533 U. S. 289, 322-323. When those consequences are, from the defendant's perspective, similarly dire, even the smallest chance of success at trial may look attractive. For Lee, deportation after some time in prison was not meaningfully different from deportation after somewhat less time; he says he accordingly would have rejected any plea leading to deportation in favor of throwing a "Hail Mary" at trial. Pointing to Strickland, the Government urges that "[a] defendant has no entitlement to the luck of a lawless decisionmaker." 466 U. S., at 695. That statement, however, was made in the context of discussing the presumption of reliability applied to judicial proceedings, which has no place where, as here, a defendant was deprived of a proceeding altogether. When the inquiry is focused on what an individual defendant would have done, the possibility of even a highly improbable result may be pertinent to the extent it would have affected the defendant's decisionmaking. Pp. 8-10.

     (c) Courts should not upset a plea solely because of post hoc assertions from a defendant about how he would have pleaded but for his attorney's deficiencies. Rather, they should look to contemporaneous evidence to substantiate a defendant's expressed preferences. In the unusual circumstances of this case, Lee has adequately demonstrated a reasonable probability that he would have rejected the plea had he known that it would lead to mandatory deportation: Both Lee and his attorney testified that "deportation was the determinative issue" to Lee; his responses during his plea colloquy confirmed the importance he placed on deportation; and he had strong connections to the United States, while he had no ties to South Korea.

     The Government argues that Lee cannot "convince the court that a decision to reject the plea bargain would have been rational under the circumstances," Padilla v. Kentucky, 559 U. S. 356, 372, since deportation would almost certainly result from a trial. Unlike the Government, this Court cannot say that it would be irrational for someone in Lee's position to risk additional prison time in exchange for holding on to some chance of avoiding deportation. Pp. 10-13.