In the case of Salvador Martinez v. Court of Appeal of California, Fourth Appellate District (1999), the U.S Supreme Court ruled that a defendant in a criminal trial does not have an absolute constitutional right to represent himself when he is also deemed mentally incompetent to stand trial. The court held that while defendants generally have a Sixth Amendment right to self-representation, this can be overridden by concerns about mental competency and ensuring fair proceedings. This decision came after Salvador Martinez, who was charged with various felonies including attempted murder and assault with a deadly weapon, insisted on representing himself despite being declared mentally unfit for trial by several psychiatrists. His request was denied by both the state appellate court and later affirmed by the U.S Supreme Court.

In the dissenting opinion for Salvador Martinez v. Court of Appeal of California, Fourth Appellate District, Justice Stevens argued that a defendant should have the right to self-representation in an appeal case if they so choose. He stated that this right is protected under the Sixth Amendment and Fourteenth Amendment's Due Process Clause. The majority ruling held that states could deny defendants their request to represent themselves on direct appeal from a conviction because it was not guaranteed by either amendment. However, Justice Stevens disagreed with this interpretation and believed it undermined individual autonomy and dignity by forcing representation upon those who did not want it. Furthermore, he expressed concern about how denying self-representation might affect indigent defendants who cannot afford counsel but are also denied public assistance due to income thresholds or other restrictions.