While the recent Democratic and Republican national conventions were mostly about impressions and feelings, successful political campaigns rely on something else: “organizing” the ground game.

For an expert tutorial on that, there may be no better source these days than Venezuelan opposition leader María Corina Machado, who organized a large part of her country of 28 million. With the help of some 600,000 volunteers, she proved conclusively that dictator Nicolas Maduro stole the recent presidential election. The United States and many other countries have refused to recognize Mr. Maduro’s illegitimate victory. The fight is far from over.

Electoral fraud is common under despotic regimes. Proving election fraud, however, is almost impossible; the regimes typically control the electoral system and the official voting documents.

Under these conditions, what Ms. Machado and her army of volunteers accomplished in the hours and days immediately following Venezuela’s July 28 presidential election was unprecedented—producing real-time voting tallies not only for the country as a whole but also for almost all of the country’s 30,000 voting stations.

Ms. Machado did this by creating a parallel election monitoring body similar to the regime-run National Electoral Council. The organization, which took advantage of the rules established by the Maduro regime, published a verifiable national vote count using official voter tally sheets.

Venezuelans vote electronically. Once voters pick their candidates, the machine prints a ballot with the name and political party of the chosen candidates, which voters then place in a ballot box. At the end of the process, the machines print tally sheets with the results of the respective precincts; these tally sheets are sent to the NEC, which compiles the totals and announces the results. Each tally sheet has a unique QR code and a digital signature and must be signed by the citizens called to serve at the polling stations and by the candidates’ representatives, who are legally entitled to obtain physical copies of the tally sheets.

The Venezuelan opposition was ready when the Maduro-controlled NEC announced that the dictator won 51.2% of the vote against opposition candidate Edmundo Gonzalez’s 44.2%. They were ready because they had obtained official copies of 83.5% of the voter tally sheets, all bearing the legal codes and digital signatures printed by the machines.

The tally sheets showed that Mr. Gonzalez had won 67% of the vote and Mr. Maduro just 30%. Even if Mr. Maduro had obtained 100% of all the votes in the precincts, for which the opposition hadn’t secured tallies, Mr. Maduro still would have lost in a landslide. Interestingly, Mr. Gonzalez was a late stand-in for Ms. Machado, who had competed in and won the primaries but was disqualified from the final election by the regime.

The opposition’s election night surprise came down to organization. Some 25 years ago, before going into politics—and several years before Mr. Maduro’s predecessor, Hugo Chavez, took control of the once-prosperous country—Ms. Machado had established a public interest organization, Sumate, devoted to popular sovereignty and monitoring elections.

Using that experience, Ms. Machado organized, in the weeks leading up to the election, what became known as Operation 600K: raising an election integrity army of 600,000 volunteers, organizing them into 60,000 groups of 10, and training them on how the system works.

On Election Day, the volunteers were ready, scrutinizing the voting process from start to finish—shielded by scores of fellow citizens who brought food and water—determined to remain at polling stations until the opposition candidates’ representatives received copies of the vote tallies to which they were entitled.

This meant having enough people at each polling station to protect the voting against regime thugs sent to intimidate volunteers and party representatives and putting pressure on the military, whose job it was to “safeguard” the original tallies and who, in many polling stations, would likely try to prevent the opposition from leaving with tally copies.

Many of the organizing activities took place behind the scenes. The dictatorship was clearly taken by surprise, as Ms. Machado’s civilian army acted with discipline, coordination, speed and efficiency to collect certified vote tallies for 83.5% of the polling stations (with many soldiers quietly collaborating by not standing in the way).

The technological sophistication of Operation 600K also played a crucial part. The volunteers transmitted, digitized and uploaded most of the tallies and the total vote count soon after the regime, acting in desperation, announced that the electoral system had been hacked (by hackers in North Macedonia, of all places), barred opposition witnesses from attending the National Electoral Council’s final vote count—as they are legally entitled to do—and announced to the world that Mr. Maduro had won.

Since the election, the regime has unleashed an unspeakable terror campaign against those who made this feat possible.

No matter how many people Mr. Maduro and his thugs kill, torture or send to prison for defending liberty, they will never be able to destroy the unprecedented achievement of Venezuela’s quiet heroes—and their lesson for the world: If you think an election is being rigged, be prepared to prove it.