Mbarka Brahmi moves through the bustling market with a rolling gait, greeting men, embracing women and pressing small cards with her candidate number and logo into their hands. It is a low-key campaign, but most people greet her by name in this small agricultural town where she grew up.

“I have faith in you,” she says to one man. “You do not need to ask,” he replies. “We are with you.”

Mrs. Brahmi, 47, a mother of five, is campaigning in Tunisia’s parliamentary election Sunday for the seat of her husband, Mohamed Brahmi, the left-wing politician whose assassination by an Islamist extremist group last year sent Tunisia into a political crisis. Despite her initial reluctance to enter public life, she has emerged unexpectedly from his shadow as a fearless political campaigner in her own right.

She has proved a scathing critic of Ennahda, the party that led the government at the time of her husband’s death, accusing it of leniency toward Islamist extremists and of failing to act when warned of threats against Mr. Brahmi — as well as complicity in his assassination. Ennahda has denied any involvement, but she remains unconvinced.

Like her husband, she is a Muslim, but believes in a separation of politics and religion and opposes political Islam. She has excoriated extremists, including a neighboring preacher in Ben Aoun, for importing Wahhabi fundamentalism from Saudi Arabia and radicalizing scores of young Tunisians, leading them toward violence and insurgency.

Yet she is unlike most of Tunisia’s secularists, who are often westernized urban sophisticates. She is a salt-of-the-earth peasant, who leans over a donkey to talk to a farmer, and weeps as a traditional storyteller in the market recites a poem lauding the bravery of her husband.

“Her father was also a militant,” who fought for independence against the French colonial power, said Hssine Abidi Abdili, an elderly man who greeted her in the market.

Both she and her husband are from Sidi bou Zid, the birthplace of the popular uprising that overthrew President Zine el-Abidine Ben Ali and set off the Arab Spring. They were both involved in underground politics for years under the rule of Mr. Ben Ali, supporting strikes and discussing politics for hours at the home of her brother, Khaled Aouainia, a human rights lawyer and political activist in Sidi bou Zid. “That was our daily bread,” she recalls.

She is representing the Popular Front, the left-wing political alliance that Mr. Brahmi helped form after the revolution. It was hit by two political assassinations last year. Its popular leader, Chokri Belaid, was assassinated in February, and Mr. Brahmi five months later. The police later found the same extremist group used the same gun for both murders.

“I wanted to continue the message of all the martyrs of the Popular Front, especially of my husband,” Mrs. Brahmi said. “I also believe in the role of women in the political process. Women are capable of being leaders. We were in the revolution and in the protests against the government last year.”

The revolution was driven by poverty and the sense of marginalization in the regions, she said. “This region is especially deprived,” she went on. “We have villages that are completely primitive. The resources for normal life do not exist. There is no water even and without water they cannot do anything.” Her job would be to compel the government to meet its obligations, in particular digging deeper wells, she said.

She sits on the floor of her brother’s home, resting swollen ankles and an aching back after a day of campaigning, but makes a face when asked why she does not just stay at home with her children, including an 11-year-old who has autism.

“I am not doing it for me, because it is a burden,” she says. “Definitely in my heart I am against it. I am doing it for Mohamed, my husband, and for the people of Tunisia and especially of Sidi bou Zid.”