Fadlallah had a wide following, not just in Lebanon but among Shia Muslim communities in the Gulf and Central Asia.
Many of his sermons, widely distributed on audiotapes in Lebanon the 1980s, helped to spark increased political awareness among Lebanon's Shia Muslim population.
Critic of US and Israel
Fadlallah was often described as the "spiritual guide" of Hezbollah, a Shia Lebanese political party. However, he never held a role within the organisation.
He did support some of its actions, endorsing suicide attacks against Israel and issuing a ruling in 2009 that forbade normalised relations with the Jewish state.
Fadlallah died in a Beirut hospital after being admitted with internal bleeding [AFP]
At the same time, he condemned other suicide attacks that targeted civilians, like the Moscow subway bombings earlier this year.
He also condemned the September 11, 2001, attacks on the US, saying they were "not compatible with sharia law".
His outspoken political views made him a target.
A 200kg car bomb exploded near Fadlallah's Beirut home in 1985. He was unharmed, but dozens of people were killed in a nearby apartment building, which was demolished by the blast.
Bob Woodward, an American investigative journalist, linked the blast to the US Central Intelligence Agency, though US officials have long denied any involvement.
Fadlallah was also a staunch critic of US foreign policy in the Middle East, accusing it of bias in favour of Israel.
"I have not found in the whole long history of the Arab-Israeli conflict even one neutral American position," Fadlallah said in a 2009 interview with the Wall Street Journal.
He wrote a letter last year to Barack Obama, the US president, in which he accused US policies of contributing to "the loss of the Palestinian cause".
Relatively liberal social views
While the West criticised him for his politics, conservative Islamic scholars often condemned Fadlallah for his moderate views.
Fadlallah was widely known for his views on women, describing men and women as equals, and issuing a ruling in 2007 which encouraged women to defend themselves against violence. He also issued a ruling banning female circumcision.
His extensive charitable works added to his popularity. Fadlallah established a network of schools and orphanages in Shia suburbs of Beirut and in southern Lebanon.
Fadlallah initially supported Iran's revolution, but later became a critic of Khomeini [AFP]
Fadlallah was an early supporter of the Iranian revolution and of Ayatollah Ruhollah Khomeini, Iran's first supreme leader.
But he eventually became a critic of the concept of wilayat al-faqih, the Iranian system of government in which the top Shia religious leader exercises absolute authority.
"[He] now argues that no Shia religious leader, not even Khomeini and definitely not his successor, Ayatollah [Ali] Khamenei, has a monopoly on the truth," Vali Nasr, an Iranian-American academic, wrote in his book The Shia Revival.
"Like all other believers, says Fadlallah, leaders are fallible and open to criticism."
His relationship with Hezbollah also grew strained as the group increased its ties to Iran.
His son, Jaafar Fadlallah, has been running many of his father's affairs for the last few months.
'A major loss'
Thousands of Fadlallah's followers gathered outside his mosque on Sunday in the Beirut suburb of Haret Hreik. Many wept and carried banners. Hezbollah's television station, Al-Manar, started broadcasting Quranic verses.
Saad Hariri, the Lebanese prime minister, called Fadlallah "a voice of moderation and an advocate of unity" for the Lebanese people.
Fadlallah's death was also mourned in Iraq, where some members of the large Shia community follow his teachings.
Ali al-Adeeb, a senior member of the Dawa party, called Fadlallah's death a major loss to the Islamic world.
"It will be hard to replace him," al-Adeeb said.