His thirty-two years on the Supreme Court put him among the top dozen of all justices for length of service. At the time of his death, he was the third longest serving Justice in the history of the Court, and he is sixth in length of service among all Justices who served before the twentieth century. He wrote about 240 majority opinions and another sixty or so separate, concurring, and dissenting opinions. And he is about as obscure a justice as we can find. Few Justices have worked so hard, for such a long period of time, and had so little impact on the Court. His importance is complicated by the fact that while on the Court he was constantly running for president, and was "in play" in every election but one from 1832 to 1860. McLean's most significant contributions on the Court involved economic issues, slavery, and the rights of free blacks. He provided a counter-balance to the pro-slavery jurisprudence of the Taney Court majority while also defending the nationalist economic jurisprudence of the Marshall Court in the face of the Taney majority's anti-nationalist economic jurisprudence.