He was also found guilty of commanding a "terrorist organisation", a reference to Palestinian resistance attacks against Israeli occupation.
The court, however, acquitted Barghuthi on charges relating to 33 attacks, saying there was no evidence proving his involvement.
Barghuthi has all along rejected Israel’s right to try him, arguing that Israel is an occupying power and the Palestinians are victims of an immoral military occupation that dehumanizes and denies them basic human rights, including the right to life.
He reportedly told the judges "this trial is as illegal and immoral as your occupation of my country is illegal and immoral. Instead of trying me, you should try your soldiers and officers who slaughtered scores of innocent children and women in Rafah yesterday".
On Wednesday, Israeli forces killed nearly two dozen Palestinians, many of them women and children, in Rafah when an attack helicopter fired two missiles at a peaceful demonstration protesting against Israel’s week-long rampage in southern Gaza.
The Palestinian Authority has strongly denounced the conviction of Barghuthi, calling it "illegal, immoral and unjust".
"Marwan Barghuthi is a fighter for freedom and justice and true peace. What really needs to be on trial is this criminal Israeli occupation," said Palestinian Minister of Labour Ghassan al-Khatib.
Al-Khatib said the PA would try to mobilise international human rights organisations to pressure the Israeli government to "put an end to this mockery".
Like many other observers, al-Khatib said that trial of Barghuthi - in both legal and human dimensions - would enhance the Palestinian lawmaker’s popularity in the Palestinian street.
"I am against killing innocent people. But I am proud of the resistance against the Israeli occupation. To die is better than living under occupation"
imprisoned Fatah leader
"In Palestine, a leader’s popularity is almost solely dependant on the extent to which he is involved in the national resistance to the occupation. And I can say that Marwan is an icon in this regard."
Arab Knesset member Ahmad Tibi, who attended the court session, said he expected a "hefty sentence" to be handed to Barghuthi.
"This trial epitomises the Israeli occupation and persecution of the Palestinians. It is an illegal and immoral trial from the beginning to the end. Marwan Barghuthi and his tormented people ought to try this diabolic occupation regime, not the other way around."
Calling the trial "farcical" and "theatrical", Tibi accused Israel of turning logic upside down.
"In the normal order of things, the court should try those child killers in Rafah instead of hounding a victim of the Israeli occupation. However, we are talking about a justice system with a name but without substance. It is the justice of the occupation."
Barghuthi’s extended trial has already made him so much of a symbol of the ongoing Palestinian Intifada that many Palestinians have begun to compare him to Nelson Mandela, the former President of South Africa and historical leader of the African National Council.
"As a political prisoner, his popularity has surged more than ever before to the level of a Nelson Mandela," said Fatah lawmaker Qaddura Faris told reporters outside the courthouse.
Tibi agreed. "I am convinced that Marwan will re-emerge stronger, I would say much stronger. This trial, unjust as it is, will be a crown of dignity and patriotism on his forehead."
Israeli occupation soldiers who
killed these civilians not on trial
However, for Atif Udwan, Professor of Political Science at the Islamic University of Gaza, the road to succeed Arafat will not be paved with flowers for Barghuthi.
"There is no doubt that his popularity will rise considerably. But this is not the same as saying that he will be elected to succeed Yasir Arafat any time soon," Udwan told Aljazeera.net.
Waiting for freedom
He argued that as long as Sharon and the Likud continued to "call the shots" in Israel, it was greatly unlikely that Barghuthi would see the light soon.
"I don’t expect that he would be a free man for several or even many years to come."
Asked if he expected that Israel might be forced to free him in the context of a prisoners’ swap deal, or under American and European pressure, Udwan recognized the possibility.
However, he pointed out that it was likely that Barghuthi would lose much of his popularity if his freedom was to be obtained through an American intervention.
"If the Americans pressure Israel to release him, then many Palestinians would begin to raise doubts and draw question marks about him."
Barghuthi, 43, repeatedly condemned attacks on civilians, Israelis and Palestinians alike.
Last year, during a court hearing, he reportedly told Israeli prosecutors that resistance was not terror but rather a personal, human and national duty upon the oppressed.
"I am against killing innocent people. But I am proud of the resistance against the Israeli occupation. To die is better than living under occupation."