By all accounts, the first time an Israeli met Yasser Arafat was in July 1982, after Uri Avnery — a white-haired war veteran, left-wing politician and muckraking journalist — boarded the Palestinian leader’s armored Mercedes in the streets of West Beirut.

The car swerved through the alleyways of a city under siege, one month into an Israeli invasion of Lebanon, and ferried Mr. Avnery to an ordinary apartment building where he spent 2½  hours interviewing the Palestine Liberation Organization chairman, a man many Israelis deemed a terrorist.

Accompanied by a German television crew, they discussed the possibility of peace in the Middle East and, according to a report in Britain’s Independent newspaper, bonded over a game of chess.

“There was a joke about Mr. Arafat not being married,” Mr. Avnery later told The Washington Post. “I said if he would marry an Israeli girl it would solve the whole problem. He said if it would solve the problem, he would do it that day.”

As scenes of his meeting with Arafat aired on Israeli television, Mr. Avnery returned home to face accusations of treason. The country’s attorney general later said no crime had been committed, but the episode cemented Mr. Avnery’s reputation as a political renegade and leading advocate of “two states for two nations” — a position that often put him at odds with Israeli officials.

When he died Aug. 20 at 94, at a hospital in Tel Aviv after suffering a stroke, Israeli President Reuven Rivlin called him “the eternal opposition figure” in a tweet, whose struggle for free speech “paved the way for Israel as a young country.”

Mr. Avnery was a dominant and divisive figure in Israel, where he called for secularism in the country’s politics, negotiations with the Islamist group Hamas, recognition of the right of Palestinians to establish their own state and shared control of Jerusalem.

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Once dubbed “Government Enemy No. 1” by the chief of Israel’s internal security service, he spent four decades as editor in chief of the news magazine Haolam Hazeh (This World), a now-defunct weekly that published exposés of government corruption alongside left-wing political columns and, on its back cover, photos of naked women.

“He ran one of the few truly independent and unabashedly critical newspapers in the state’s early years,” said Haviv Rettig Gur, senior analyst with the Times of Israel. “Uri is one of the first serious journalists who introduced into our profession in Israel an ethos of independent criticism. Though he was on the deep left on the issues, he could critique left-wing parties as readily as right-wing ones.”

In his youth, the German-born Mr. Avnery championed an ideology known as revisionist Zionism, which called for a Jewish state that would extend from the Mediterranean through the modern state of Jordan. His views shifted leftward while fighting for Israeli independence, and — after writing a best-selling war book — he became one of the first prominent Israelis to openly call for a two-state solution.

When Mr. Avnery came out in support of Arafat, insisting that the Palestinian leader sought peace, he effectively “pioneered . . . the argument at the heart of the Oslo project,” said Gur, referring to the 1990s negotiations between Arafat and Israeli Prime Minister Yitzhak Rabin.

That peace process has long since stalled, although Mr. Avnery expressed confidence that a breakthrough would occur. He had, he told the Independent in 2012, “the misfortune of being an incorrigible optimist,” as his views were increasingly out of step with Israel’s political leadership and even the country’s political left.

“He was ahead of his time and then lagged behind it,” said Diana Buttu, a former legal adviser to the Palestinian negotiating team. “Now the conversation among left-wing Israelis is no longer about two states. It’s about challenging and actually denouncing Zionism, acknowledging the wrongs of the past. . . . His death, in a lot of ways, marks the end of the two-state solution — he was the last activist I know of that was really calling for it.”

Mr. Avnery was born Helmut Ostermann in Beckum, Germany, on Sept. 10, 1923, and raised in Hanover, where his father worked in finance. The family immigrated to what was then the British mandate of Palestine when Helmut was 10, months after Adolf Hitler came to power.

They soon slipped into poverty, and Mr. Avnery left school at 14 to work as a clerk in a law office. He also joined the Irgun, a paramilitary group that, he told Haaretz, “planted bombs in markets in Jaffa and in Haifa, which killed dozens of women and children.” He left the organization after several years and wrote in a 2014 memoir, “Optimistic,” that he “learned that the difference between a freedom fighter and a terrorist depends on your perspective.”

Mr. Avnery served with an Israeli commando unit during the country’s 1948 war of independence, during which he was wounded by machine-gun fire on the Egyptian front. About that time he also adopted his last name, Hebraizing the name of his brother Werner, who died during the war.

Acclaim for Mr. Avnery’s journalistic war book, “In the Fields of the Philistines” (1949) was followed by dismay at its sequel, “The Other Side of the Coin” (1950), which alleged wartime atrocities. It brought Mr. Avnery his first dose of public scorn, which continued in earnest after he acquired Haolam Hazeh in 1950.

The magazine’s circulation was never more than 25,000, according to the Jerusalem Report, although Mr. Avnery said each issue found its way to about 150,000 readers. That figure apparently did not include David Ben-Gurion, Israel’s first prime minister, who reportedly referred to it only as “that certain weekly,” refusing to use its name.

Before Mr. Avnery sold the magazine in 1990 — it closed several years later — he and its newsroom inspired frequent controversy and sometimes outright violence. He said the publication’s offices were bombed three times, that fingers on both his hands were once broken during a nighttime ambush, that the newsroom’s archives were burned down in 1972 and that three years later he was stabbed “by an alleged lunatic” who tried to kill him.

A defamation law that Mr. Avnery said was targeting the magazine led him into electoral politics. Establishing a small new political party, he was elected to the Knesset in 1965, reelected four years later and — after losing at the polls in the aftermath of the Yom Kippur War — served part of a third term, from 1979 to 1981.

Mr. Avnery was out of office when he made contact with Arafat, at a meeting that was closely monitored by Israeli forces. This year, in the book “Rise and Kill First,” journalist Ronen Bergman reported that an Israeli special-ops team was organized to assassinate Arafat and unsuccessfully attempted to follow Mr. Avnery to the meeting in an effort to ferret out the Palestinian leader’s location.

The group, code-named Salt Fish, lost Arafat’s car “in the alleys of south Beirut,” Bergman reported, and had planned to kill Mr. Avnery as well if necessary. That fact was long unknown to Mr. Avnery, who in 2003 joined Arafat in Ramallah, during the second intifada, to act as a “human shield.” He believed — apparently incorrectly — that his presence might have prevented a possible assassination of Arafat by Israel.

With his wife, the former Rachel Gruenbaum, Mr. Avnery founded the activist group Gush Shalom (Peace Bloc). Together they received the Right Livelihood Award, known as the “Alternative Nobel Prize,” in 2001, when they were cited “for their unwavering conviction, in the midst of violence, that peace can only be achieved through justice and reconciliation.”

Mr. Avnery’s wife died in 2011. They had no children, and he said his political actions sometimes caused tension with the rest of his family. When his mother died, she scorned him in her will, reportedly writing that he would receive no inheritance “since he didn’t take care of me and instead went to visit that murderer Yasser Arafat.”

In recent years, Mr. Avnery wrote regular columns for Haaretz, most recently condemning the newly passed “nation-state” law, which formally declares Israel a homeland for the Jewish people. Calling it a “semi-fascist” piece of legislation, he wrote that its outcome was clear: “No democracy. No equality. A state of the Jews, for the Jews, by the Jews.”