ANSWER: I might phrase it a bit differently. He read the Judiciary Act as purporting to confer jurisdiction on the Supreme Court in any case in which mandamus is the proper remedy. Because mandamus was the proper remedy in Marbury's situation, then the Act attempted to grant the Court jurisdiction. But this was not a case that fell within the original jurisdiction of the Supreme Court as defined in Article III. Hence, there was a constitutional problem.
QUESTION: Unofficially, Marshall interpreted the Act in an overbroad manner. The Act appears to be giving the Supreme Court jurisdiction in cases of appeal, whereas he interprets it to say that the court always has original jurisdiction over writs of mandamus.
ANSWER: That is a fair criticism. Marshall's interpretation of the Judiciary Act is not the most intuitive (though it has its defenders). To me, the relevant language appears either (a) to refer to what the Court can do when exercising its appellate jurisdiction, or (b) more generally, define the remedies that the Court is authorized to issue, provided the Court already has jurisdiction over the case. Had Marshall adopted either of these readings, of course, he would have been forced to conclude that the Court lacked subject matter jurisdiction before reaching the constitutional question. As a result, the Court could not have discussed at length the power of judicial review. So we are left to think that, yes, perhaps Marshall's reading of the Act was a bit disingenuous. But we do not know that for sure. He never admitted to deliberately subverting the language of the statute to reach the questions he wanted to answer.
QUESTION: Okay, I'm glad I asked, because your phrasing is where I'm confused. It seems as if you are saying that there are two subtle phases here: (1) he actually took the case because the judiciary act (as he interprets it) allows him to; and (2) once he has taken the case, the Judiciary Act (as he interprets it) presents a constitutional issue -- which allows him an opportunity to flex his judicial review muscles and review a federal law. Is that right? I think that I'm confused about what the official reason was that Marshall gave for the court to have jurisdiction. It seems like there are two things going on here.
ANSWER: There are three points that might help clarify things:
1. The Supreme Court actually had no discretion as to whether to "take" the case of Marbury v. Madison. At the very least, the Court had to determine whether it had jurisdiction. So there was no choice in at least reaching that question.
2. I think it is correct to suspect that Marshall construed the Judiciary Act as he did to enable him to reach the constitutional question. But it is important to understand that the only question the Court ever addresses in Marbury is jurisdictional. (There is some other stuff, but it is technically dicta.) The jurisdictional question, properly understood, had two parts. First, there was the statutory question: had Congress granted the Supreme Court jurisdiction in cases such as this. Marshall read the Judiciary Act as doing so (though I think that is an unsound reading). Once he resolved the statutory issue this way, he then addressed the constitutional question: was such a statutory conferral of jurisdiction consistent with Article III? Here, Marshall said no (and in the process defended the Court's power to declare such acts inconsistent with the Constitution). So both questions -- the statutory and the constitutional -- were jurisdictional, in the sense that they concern whether the Supreme Court had jurisdiction to decide Marbury's case. By getting to the constitutional question, though, Marshall was permitted to discuss judicial review.
3. Don't forget that the ultimate holding in Marbury is that the Supreme Court LACKED jurisdiction. Why? Because section 13 of the Judiciary Act, purporting to grant the Court jurisdiction, was unconstitutional. It attempted to grant the Court original jurisdiction in a case in which Article III does not permit. Thus, at the end of the day, the Court actually dismisses the case for want of jurisdiction.