Schwebel is noted for his expansive opinions in momentous cases such as Legality of the Threat or Use of Nuclear Weapons,[9] Military and Paramilitary Activities in and Against Nicaragua[10] and Oil Platforms (Islamic Republic of Iran v. United States of America).

This experience has been presented as the starting point of a career "firmly embedded in the UN firmament and ... devolved into its service, or on legal matters pertaining to it".

magna cum laude with highest honors in government from Harvard and was awarded the Frank Knox Memorial Fellowship.

Schwebel was assigned the "digging" on the case and spent countless hours going through files; however, the experience engendered a lifelong interest in international arbitration.

In September 1978, Schwebel, acting as deputy legal adviser to the U.S. Department of State, sought accountability for the mass executions committed by the Khmer Rouge.

Schwebel wrote the U.K. Foreign Office about the possibility of instituting proceedings against Cambodia before the International Court of Justice for genocide.

[17] Schwebel stated that the atrocities had apparently not been aimed at destroying, in whole or in part, a "national, ethnical, racial or religious group," as defined by the Genocide Convention, but rather those whom the Cambodian authorities deemed to be politically unsympathetic.

[18] Schwebel was a key member of the U.S. State Department team that initiated and sought to influence, through an amicus brief, the Second Circuit Court of Appeals in its hearing of the landmark case Filártiga v. Peña-Irala.

[39] He is critical of the court's inability to conclude whether or not the threat or use of nuclear weapons is lawful or unlawful in an extreme circumstance of State self-defense.

[42] Schwebel also agreed with the court that unannounced mining of Nicaragua's ports by the United States was a violation of customary international law.

Schwebel also found that the United States violated the law of war when the Central Intelligence Agency orchestrated the publication and distribution of a manual titled, Operaciones Sicologicas en Guerra de Guerillas.

[43] However, with the exceptions of Judges Shigeru Oda (Japan) and Sir Robert Jennings (UK), he disagreed profoundly with interpretation of what constitutes an armed attack, under international law, by one state on another.

[44] Schwebel, however, felt that the scale of involvement by Nicaragua crossed a threshold of what, under customary international law, would be considered an armed attack by one state on another.

He stated in his dissenting opinion that the court's majority did not thoroughly consider the prodigious evidence that Nicaragua was aggressively supporting the insurgency in El Salvador.

Scholars have written that Schwebel was inhibited, however, in making a case for his view due to the withdrawal of the United States from the proceedings and, as a result, the lack of an advocate in the court to defend U.S. policy and to attack the evidence presented by Nicaragua.

[47] In Oil Platforms (Islamic Republic of Iran v. United States), Schwebel, acting as vice president of the ICJ, issued a dissenting opinion to the court's 1996 preliminary judgement ruling that it could exercise jurisdiction over the dispute.

The United States filed preliminary objections to the court's jurisdiction and a counter-claim challenging Iran's attacks on vessels in the Persian Gulf.

In October 2010, Schwebel was appointed by the UN Secretary-General Ban Ki-moon as the chairman of the Kishanganga/Neelum River Hydro-Electric Project (Pakistan v. India) Arbitration.

In October 2007, Schwebel was appointed to a three-member tribunal tasked with determining whether or not to annul the award (on jurisdiction) rendered in the dispute between the UK registered firm Malaysian Historical Salvors and the Government of Malaysia.