The fate of the Western and Arab-backed resolution rested with Russia, Syria's closest ally, and China, another supporter.
After two weeks of negotiations and a watering-down of the original text, they decided to join the rest of the 15-member council in sending a strong message, especially to the Assad government, that food, medicine and other essentials must not be blocked to civilians caught in the three-year conflict.
"Today the council has finally shown that whatever its political differences over Syria, it was not entirely indifferent to the devastating humanitarian crisis," Britain's U.N. Ambassador Mark Lyall Grant said after the vote.
According to the United Nations, 9.3 million Syrians are in need of humanitarian assistance and 6.8 million have fled their homes but remain in the country.
The resolution does not threaten sanctions—Russia insisted that this reference be dropped from the original text. Instead, it asks Secretary-General Ban Ki-moon to report to the council every 30 days on implementation and expresses the council's intention to take "further steps" if the resolution's demands aren't fulfilled.
All Security Council resolutions are legally binding, but what remains to be seen is whether this resolution has an impact on the ground, especially since it doesn't have real "teeth."
U.N. humanitarian chief Valerie Amos expressed hope in a statement that it "will facilitate the delivery of aid to people in desperate need in Syria."
Calling the resolution a "long overdue" measure "to alleviate the worst humanitarian crisis of this generation," U.S.
"The world now needs to stand united on behalf of implementation so that there are no more broken promises, no more delays, no more coupling minor concessions with cruel and shameless attacks on civilians," Power said.
France's U.N. Ambassador Gerard Araud said implementation "depends on the goodwill of the Syrian regime and the opposition."
If the resolution's demands aren't fulfilled, he said, France will propose "further measures."
The resolution demands that all parties, especially the Syrian government, "promptly allow rapid, safe and unhindered access ...
It demands that all parties "cease depriving civilians of food and medicine indispensable to their survival." It also demands a halt to all attacks against civilians, including indiscriminate shelling and aerial attacks using barrel bombs in populated areas.
U.N. Secretary-General Ban Ki-moon told the council immediately after the vote that the resolution "should not have been necessary" because "humanitarian assistance is not something to be negotiated—it is something to be allowed by virtue of international law."
"Half the country's people need urgent assistance," he said.
The U.N. chief said it is "profoundly shocking ... that both sides are besieging civilians as a tactic of war."
"Some 200,000 people are under siege in government-controlled areas—and 45,000 in opposition-controlled areas," Ban said.
Russia and China had vetoed three previous resolutions backed by Western nations that would have pressured Assad to end the conflict, which according to activists has killed more than 136,000 people.
Russia's U.N. Ambassador Vitaly Churkin said Moscow supported the humanitarian resolution because "many Russian considerations were borne in mind, and as a result the document took on a balanced nature.
He accused the resolution's sponsors—Australia, Luxembourg and Jordan—and its supporters of raising the humanitarian crisis in the council "only after it became clear that attempts to use a deterioration of this humanitarian situation in order to carry out a regime change was unsuccessful."
Churkin also insisted that efforts to get humanitarian access in Syria "although not as quickly as we would have liked is getting positive, concrete results."
China's U.N. Ambassador Liu Jieyi strongly urged all parties to implement the resolution "in good faith."
"China is gravely concerned at the worsening humanitarian situation in Syria," he said. "We deeply sympathize with people and we hope to see an early and prompt amelioration of the situation in Syria."
Syria's U.N. Ambassador Bashar Ja'afari Syria told the council that since the beginning of the crisis "the Syrian government was keen to improve the humanitarian situation of the people" and "it has continued to work day and night in order to perform all the humanitarian needs of its citizens."
Ja'afari added that the Syrian government is providing 75 percent of the humanitarian assistance in the country while the U.N. and other organizations have supplied only 25 percent. He accused some unnamed countries of politicizing the delivery of humanitarian aid, misleading international public opinion, and refusing to provide ambulances and wheelchairs for people with special needs.
The main Western-backed Syrian opposition group, the Syrian National Coalition, welcomed the resolution saying the international community should guarantee "full implementation."
It added in a statement that the council should be ready to take "needed legal measures if Assad's regime tried to evade or procrastinated in the implementation."
The Security Council did come together in October to approve a weaker presidential statement on the worsening humanitarian crisis.
But Amos, the U.N. humanitarian chief, said last week that the presidential statement has not delivered the results that are critically needed, calling progress on the humanitarian front in the last four months "limited, uneven and painfully slow." She backed a council resolution if it had "levers" that lead to change on the ground.
While the resolution focuses on the humanitarian situation, it also strongly condemns the increased terrorist attacks by al-Qaida and its affiliates and other terrorist groups, calls on the government and opposition to defeat the terrorists, and "demands that all foreign fighters immediately withdraw from Syria."
Churkin said Russia will ask the council to quickly move to discuss a draft document on combating terrorism in Syria.
The resolution also emphasizes "that the humanitarian situation will continue to deteriorate in the absence of a political solution."
It demands that the government and opposition work toward "a genuine political transition that meets the legitimate aspirations of the Syrian people and enables them independently and democratically to determine their own future."
In her statement Saturday, Amos stressed that ordinary people who have been bearing the brunt of the violence must be protected.
"More than anything, the conflict needs to end so that people can begin to rebuild their lives," Amos said. "Syria is in danger of losing a generation of its children. Children are the future. We must protect them."
Associated Press writer Bassem Mroue contributed from Beirut, Lebanon.