He led a band of armed rebels. She was an expert in forging documents. They robbed banks, they staged prison breaks and they were in love.

It was the early 1970s, and José Mujica and Lucía Topolansky were members of a violent leftist guerrilla group, the Tupamaros. To them, their crimes were justified: They were fighting a repressive government that had taken over their small South American nation, Uruguay.

He was 37 and she was 27 when, during a clandestine operation, they first came together. “It was like a flash of lighting in the night,” Mr. Mujica, now 89, recalled many years later of their first night together, hiding out on a mountainside.

Amid war, they found love. But just weeks later, they were thrown in prison, where they were subjected to torture and abuse. Over 13 years, they managed to exchange only a single letter. The guards confiscated the rest.

In 1985, Uruguay’s dictatorship ended. They were released on the same day, and they quickly found one another.

It was a critical moment in their extraordinary love story. After more than a decade apart, their love was still alive — and so was the shared cause that had first united them.

“The next day we started looking for a place to gather our companions. We had to start the political fight,” Ms. Topolansky, 79, said in an interview in their home last week. “We didn’t waste a minute. And we never stopped, because it’s our vocation. It is the meaning of our life.”

Over the following decades, Mr. Mujica and Ms. Topolansky became two of their nation’s most significant political figures, helping transform Uruguay into one of the world’s healthiest democracies, regularly lauded for the strength of its institutions and the civility of its politics.

They were both elected to Uruguay’s Congress, and would drive to work together on the same moped.

In 2009, Mr. Mujica, known widely as Pepe, was elected president, capping a remarkable political journey. At his inauguration, as per tradition, he received the presidential sash from the senator who had received the most votes: Ms. Topolansky. She gave him a kiss, too.

In 2017, Ms. Topolansky was named Uruguay’s vice president in a different leftist administration. At various moments, she was the country’s acting president.

At the same time, away from the spotlight, they built a quiet life on a small chrysanthemum farm outside Uruguay’s capital, Montevideo. Together they tended to their flowers and sold them at markets. They have often been spotted together in their sky blue 1987 Volkswagen Beetle or listening to tango at one of their favorite Montevideo bars.

They have said prison robbed them of their chance to have children. Instead, they have cared for countless dogs, including a three-legged mutt named Manuela who became famous for often accompanying Mr. Mujica while he was president.

They are not always romantics. In 2005, they had been living together for 20 years but were still unmarried. One night, Mr. Mujica did an interview on a national television show. “He told the journalist that we were going to get married. I was watching the show and that’s how I found out,” Ms. Topolansky recalled last week, laughing. “At this age, I just caved in.”

They were married at a simple ceremony at home. That night, they went to a political rally.

“We united two utopias,” Ms. Topolansky told a documentary filmmaker years ago. “The utopia of love, and the utopia of political struggle.”

The details of their first encounter have remained vague. Ms. Topolansky said she had provided Mr. Mujica with falsified documents. Mr. Mujica has said Ms. Topolansky was part of a team that helped him and other Tupamaros escape from prison, and he first spotted her when he stuck his head up from a tunnel.

Ms. Topolansky said the details are hard to recall for a reason. “It’s a lot like those war stories, where human relationships are distorted because of the context. You’re fleeing, you can be arrested, they can kill you. So you don’t have the regular boundaries of normal life,” she said.

But it was also those difficult conditions that lit their fire. “When you live a clandestine life, affection is really important. You give up a lot. So when a relationship and love show up, you gain so much,” she told the filmmaker several years ago.

Now they say they have entered one of their most difficult moments. In April, Mr. Mujica was diagnosed with a tumor in his esophagus. Radiation therapy has left him weak.

Last week, he sat in front a wood stove in the home they have shared for almost four decades, as Ms. Topolansky helped him put on an extra layer as the sun set. “Love has ages. When you’re young, it’s a bonfire. When you are an old man, it’s a sweet habit,” he said. “I’m alive because of her.”

Mauricio Rabuffetti contributed reporting from Montevideo.