The Egyptian diplomat has led the International Atomic Energy Agency (IAEA) during its transition from a nondescript bureaucracy monitoring nuclear sites worldwide to a pivotal institution at the forefront of disarmament efforts.
Austere and methodical, he has taken a sometimes strident line while guiding the Vienna-based agency through the most serious troubles it has faced since the end of the Cold War.
'Spade a spade'
He accused North Korea of "nuclear brinkmanship" in December 2002 after it expelled two inspectors who were monitoring a mothballed nuclear complex.
"I'm calling a spade a spade," he said at the time. "I see a very serious crisis - a country that's completely defying the world."
ElBaradei's most recent efforts
have been concentrated on Iran
He also directed the agency as it launched inspections in Iraq alongside the hunt for biological and chemical agents conducted by the UN Monitoring, Verification and Inspection Commission.
In January 2003, contradicting US intelligence reports, he said: "We have to date found no evidence that Iraq has revived its nuclear weapons programme since the elimination of the programme in the 1990s."
Most recently, it is his focus on Iran - and IAEA efforts to establish whether that country has a secret nuclear weapons programme - that has kept him in the international nonproliferation limelight.
Iran and Iraq
Iran, concerns about a nuclear black market and efforts to end North Korea's nuclear arms programme, pose "an unprecedented array of challenges to the nonproliferation and arms control regime," he said last month, as he outlined agency priorities.
ElBaradei has had to contend with US opposition to his tenure, but that ended formally last month when IAEA member nations formally approved his reappointment for a third term.
"Bear with us ... What we do is the cornerstone of all arms control activities"
Chief IAEA nuclear inspector
Much of the opposition stemmed from Washington's perception that he was being too soft on Iran for not declaring it in violation of the Nuclear Nonproliferation Treaty. That stance blocked a US bid to haul Tehran before the UN Security Council for more than two years.
He also refused to endorse Washington's contention that Iran was working to make nuclear weapons and disputed US assertions that the Saddam Hussein-led government in Iraq had an active atomic weapons programme - both claims that remain unproven, despite growing suspicions about Tehran's nuclear agenda.
Born in Egypt in 1942, ElBaradei earned a bachelor's degree in law in 1962 at the University of Cairo.
After a stint in the Egyptian Ministry of Foreign Affairs, he received a doctorate in International Law at the New York University School of Law in 1974, and later became an adjunct professor there.
He married Aida Elkachef, a nursery school teacher, and had two children: Laila, a lawyer, and Mostafa, a biotechnologist.
Tall, dapper and shy, ElBaradei joined the IAEA in 1984 and rose from within the ranks of the 139-nation agency.
As pressure mounted to act in Iraq, ElBaradei blossomed in the hothouse of media scrutiny. The man who once stumbled before television cameras started to speak in soundbites, growing ever bolder in his statements.
But he held fast to the nuclear agency's guiding principle that science and research needed to be respected - even as the swirling pressure to act closed in.
As the agency's critics argued the IAEA was moving too slowly to counter the new nuclear threats, ElBaradei appealed for patience, arguing that scientific examination was critical to the agency's work. "Bear with us," he said. "What we do is the cornerstone of all arms control activities."