It was perhaps only fitting that Obama had the last say. His push for a thaw with Tehran, a longtime US foe, dates back to before his presidency, and no other foreign policy issue bears his personal stamp more since he took office in early 2009.
Behind the risky diplomatic opening is a desire for a big legacy-shaping achievement and a deep aversion to getting America entangled in another Middle East conflict - motives that override misgivings to the Iran deal expressed by close allies Israel and Saudi Arabia.
That may explain why Obama, even as he left the troubleshooting to Secretary of State John Kerry and gave him much of the credit for securing the diplomatic coup, has taken "ownership" of the Iran issue like no other.
His engagement - both in private and in public and according to aides, at a level of minute detail - is in contrast to a more aloof approach as Egypt came under military rule and Syria descended into civil war.
"It's the top item on his foreign agenda for the rest of his term," a source close to the White House's thinking said of the Iran issue. "He doesn't want to leave anything to chance."
The stakes are enormous for Obama. If the talks break down and Iran dashes to build an atomic bomb before the West can stop it, he could go into the history books as the president whose naivete allowed the Islamic Republic to go nuclear.
The breakthrough with Iran is also worrying the many pro-Israel members of Congress, including heavyweights in his own Democratic Party like Senator Charles Schumer.
Last weekend's Iran pact - a preliminary agreement on modest sanctions relief in exchange for temporary curbs on Iran's nuclear activities - was no case of accidental diplomacy.
Obama promised to seek direct engagement with Iran and other US enemies during the 2008 presidential campaign, drawing accusations from Republicans that he was promoting appeasement.
He then used his first inaugural address in 2009 to offer to extend a hand if the Iranian leadership would "unclench their fist." After being snubbed, he galvanized international support for crippling sanctions that ultimately forced Tehran into the latest negotiations.
Obama instructed his aides to arrange the historic telephone conversation he had with Iran's relatively moderate new president, Hassan Rouhani, in September, and authorized secret bilateral talks that laid the groundwork for the more formal Geneva rounds between Iran and world powers, US officials say.
On Saturday, Kerry spoke by phone to Obama from Geneva to discuss the outstanding issues in the final tense stages of negotiations, a senior State Department official said. "This went all the way up to (Obama) personally approving the final language," the official said.
While it may not be unusual for Obama to cast his trained legal eye on government-to-government agreements, his close attention to the wording of the deal-in-the-making underscored the sensitivity of the breakthrough document and his determination to get it right.
Once the deal was signed in Switzerland, Obama stepped in front of the cameras at the White House in a rare late-night appearance and hailed it as "an important first step toward a comprehensive solution that addresses our concerns."
It was a chance to tout a foreign policy accomplishment at a time when Obama is struggling with a flawed healthcare rollout and low approval ratings at home.