Organisers said a record 500,000 people attended Saturday’s rallies, making them some of the “biggest in Israeli history”.
Media in Israel put the turnout at 250,000 to 300,000 people.
The demonstrations come as Netanyahu’s government prepares to press on with its legislative agenda next week, shunning calls for a pause to allow for negotiations on the divisive judicial reforms.
“I’m demonstrating because the measures that the new government wants to take represent a real and immediate threat to Israeli democracy,” one protester, tech entrepreneur Ran Shahor, told the AFP news agency in the coastal city of Tel Aviv.
“It’s not a judicial reform. It’s a revolution that [is] making Israel go to full dictatorship and I want Israel to stay a democracy for my kids,” Tamir Guytsabri, 58, told the Reuters news agency.
Some 200,000 Israelis rallied in Tel Aviv, while 50,000 people protested in the northern city of Haifa and 10,000 in Beersheba — the biggest yet in both — according to Israeli media.
The rallies broke up without major incident, although police arrested three protesters who were blocking traffic on Tel Aviv’s ring road.
The uproar over the legal changes has plunged Israel into one of its worst domestic crises. Beyond the protests, which have drawn tens of thousands of Israelis to the streets and have recently become violent, opposition has surged from across society, with business leaders and legal officials speaking out against what they say will be the ruinous effects of the plan.
The legislation would give more weight to the government in the committee that selects judges and would deny the Supreme Court the right to strike down any amendments to so-called Basic Laws, Israel’s quasi-constitution.
These provisions have already been endorsed by legislators at first reading.
Another element of the reforms would give the 120-member parliament power to overrule Supreme Court decisions with a simple majority of 61 votes.
Critics say the changes will destroy the country’s system of checks and balances and concentrate power in the hands of the prime minister and his allies.
Some also say Netanyahu, who is on trial for corruption, is driven by personal grievances and that he could find an escape route from the charges through the overhaul.
Netanyahu denies wrongdoing and says the legal changes have nothing to do with his trial.
Israeli President Issac Herzog — who, in his largely ceremonial role, has tried to broker dialogue — on Thursday called on the governing coalition to halt the legislation, dubbing it “a threat to the foundations of democracy”.
The chair of parliament’s law committee, Simcha Rotman, however, has scheduled daily hearings on parts of the government’s reforms from Sunday through Wednesday ahead of votes.
Justice Minister Yariv Levin has said the coalition plans to pass key elements of the reforms before parliament goes into recess on April 2.
The judicial overhaul is a cornerstone of Netanyahu’s administration, an alliance with ultra-Orthodox Jewish and extreme-right parties which took office in late December.