On June 12, 2008, the U.S. Supreme Court issued a landmark decision in favor of the petitioners in Boumediene v. Bush, (06-1195), finding that the detainees held at Guantánamo Bay Naval Base have a right to challenge their detention in U.S. courts. The Supreme Court struck down the provisions of the Military Commissions Act of 2006 that stripped the federal courts of jurisdiction to hear habeas corpus petitions filed by Guantánamo detainees, holding that these provisions violate the Suspension Clause of the U.S. Constitution. "The laws and Constitution are designed to survive, and remain in force, in extraordinary times," Justice Kennedy wrote for the majority.

Mayer Brown filed the sole amicus brief in support of the petition for certiorari in Boumediene, an omnibus brief on behalf of all of the amici who had urged the Supreme Court in Rasul v. Bush, 542 U.S. 466 (2004), to uphold the detainees' right to file habeas corpus petitions challenging their detention. After the Supreme Court agreed to hear Boumediene, Mayer Brown attorneys, in conjunction with the Brennan Center for Justice at NYU Law School, coordinated the over twenty amicus briefs filed in support of the Boumediene petitioners on the merits. Mayer Brown's own amicus in Boumediene, filed on behalf of retired military officers, argued that the Combatant Status Review Tribunals ("CSRTs") created in the wake of Rasul v. Bush and Hamdi v. Rumsfeld, 542 U.S. 507 (2004), do not comply with U.S. military law principles or the Geneva Conventions, and that failing to provide Guantánamo detainees with meaningful judicial review of their imprisonment would imperil U.S. service men and women captured overseas. The Mayer Brown attorneys on the amicus brief in Boumediene were Gary Isaac, Philip Lacovara, Jim Schroeder, Catherine Bernard, Jeffrey Berger, and Stephen Kane. 

Since the fall of 2003, Mayer Brown lawyers have been actively involved in every phase and aspect of the high-profile habeas corpus litigation challenging the US government's detention of alleged "enemy combatants" at Guantánamo and elsewhere. In all, Mayer Brown attorneys have submitted six amicus briefs in the U.S. Supreme Court in the detainee litigation. In the Fall of 2006, Mayer Brown attorneys also submitted an amicus brief in the Fourth Circuit on behalf of former senior Justice Department officials, including former Attorney General Janet Reno, in al-Marri v. Wright, a case challenging the President's authority to hold a legal alien arrested at his home in Illinois as an "enemy combatant." In addition, Mayer Brown attorneys in 2005 and 2006 helped lead the lobbying efforts by counsel for the detainees at Guantánamo in opposition to the jurisdiction stripping provisions of the Detainee Treatment Act of 2005 (which the Supreme Court, in Hamdan v. Rumsfeld, 548 U.S. 557 (2006), held inapplicable to pending habeas corpus petitions) and the Military Commissions Act of 2006 (which the Supreme Court struck down in Boumediene)

Mayer Brown has been recognized by the Center for Constitutional Rights, the National Legal Aid & Defender Association, and the Southern Center for Human Rights, for its work on the Guantánamo detainee litigation.