After five hours of intensive negotiations with Iran's nuclear point-man -- national security chief Hassan Rowhani -- ElBaradei announced Iran had pledged to file a new report on its nuclear activities before the body next meets in June.
He said Iran also agreed to a tough action plan and timetable aimed at clearing up serious questions over its bid to generate atomic power -- seen by the United States and Israel as a convenient cover for weapons development.
"Today I was reassured by Dr. Rowhani that Iran is committed to continue to actively cooperate," said the director general of the International Atomic Energy Agency (IAEA).
"I can tell you that I am quite satisfied," ElBaradei added, saying his talks had yielded "welcome and positive steps".
Before going into a series of closed-door talks, ElBaradei warned that the IAEA's 35-member board of governors was becoming "impatient with Iran" after the Islamic republic failed to give a comprehensive declaration of its nuclear activities and has delayed crucial inspections.
Last October Iran gave the IAEA what it asserted was a complete declaration of its nuclear activities. It was later found to have made a number of omissions, including its acquisition of designs for sophisticated P-2 centrifuges that can enrich uranium to bomb-grade levels that are way above those required for atomic energy reactors.
In December, it signed the additional protocol to the nuclear Non-Proliferation Treaty (NPT), which sets tougher conditions for IAEA inspections and commits the country to filing a new and more detailed declaration to the Vienna-based agency within six months.
"Dr. Rowhani assured me that we will get some important information before the end of this month and that we would also hope to get information under the additional protocol by mid-May," ElBaradei said.
"We agreed on an action plan with timetable on how to move forward with the major outstanding issues," he added.
Sources close to the talks said the principal remaining question covered the P-2 centrifuge and accounting for traces of weapons-grade uranium found by the IAEA at two sites here.
Iran asserts the traces came into the country on equipment bought on the black market from Pakistan. To verify this ElBaradei said he hoped Pakistan would allow the IAEA to take so-called "environmental samples" there.
But despite the latest in a line of Iranian promises to fully comply, there appeared to be some sticking points. Notable was how much work Iran should be allowed to conduct on the sensitive nuclear fuel cycle while the complex IAEA investigation is still running.
Iran's atomic energy chief, Gholam Reza Aghazadeh, said Iran had refused a call from ElBaradei to delay its resumption of uranium conversion work -- or producing the precursors for the enrichment process -- at a facility in the central city of Isfahan.
Aghazadeh said sardonically that he had instead expected the IAEA to "congratulate us on the success we have had in mastering this technology."
Iran insists such work does not violate its suspension of enrichment-related activities. That move has been criticised by Britain, France and Germany -- who stepped in last year to secure Iranian cooperation with the IAEA -- as likely to further damage confidence.
And while Aghazadeh announced to reporters that Iran would also stop the construction and assembly of centrifuges used to enrich uranium as of April 9, it was a repeat of a promise made earlier this year.
ElBaradei said a team of IAEA inspectors would arrive in Iran on April 12 to verify the suspension of uranium enrichment was being respected.
For his part, Rowhani asserted that Iran did not have a "hidden parallel programme, because when someone signs the additional protocol inspectors can see everything."
And he said Iran would "react firmly" if, after the IAEA meeting in June, the Iran dossier still looked as if it was a long way off from being settled.
"But personally I do not think Iran will leave the NPT," he added, while asserting Iran's desire to be "a member of the club of countries that enrich uranium".
If Iran is judged to have failed to meet IAEA demands, the IAEA board could declare the country in breach of the nuclear Non-Proliferation Treatyand refer the matter to the matter to the UN Security Council, which could choose to impose punishing sanctions.
But with a new declaration to verify and more environmental samples to examine, analysts say the fruits of ElBaradei's latest visit are unlikely to remain unclear until after the June meeting.