On a peaceful Monday morning in March 2018, a Senegalese street vendor named Idy Diene was murdered on the Vespucci bridge in Florence. The man who fired the six fatal shots was an Italian pensioner who told the police he had shot randomly at the first person he encountered. He had previously attempted to take his own life.

Antonella Bundu, 49, was one of the first people to arrive at the scene. She burst into tears when she was told that under the blood-stained sheet lay Diene. She had come to know him well, watching him set up and take down his makeshift table of cigarette lighters, tissues and umbrellas.

That afternoon she took part in the protests led by the Senegalese community in Florence. Diene had become the most recent victim of a series of attacks against Africans in Italy as anti-immigrant propaganda, spread in part by the far-right leader Matteo Salvini, continued to circulated in mass media.

Since that day, the number of racially motivated attacks against migrants has risen sharply in Italy, tripling between 2017 and 2018, and Salvini has become interior minister. One year after Diene’s death, spurred on by the climate of intolerance and racism that has spread throughout the country, Bundu has decided to run for mayor of Florence. The daughter of a Florentine mother and a Sierra Leonean father, she has become the first black female candidate for mayor of a large Italian city.

She is the lead candidate in a coalition of radical-left parties including Potere al Popolo (Power to the People) and Rifondazione Comunista (Communist Refoundation). The vote will be held at the same time as the European elections on 23-26 May.

“Until a few months ago I never imagined I could take on such a role,” Bundu told the Guardian. “Then a movement tied to the left invited me to speak at the Alfieri Theatre in Florence. I was given one word on which to improvise a seven-minute speech. The word was ‘black’. Without hesitation I poured out about what was happening in Italy. I spoke about myself, my story. They must have liked my monologue, because they immediately asked me if I’d be interested in running for mayor’s office.”

Antonella Bundu in Florence. Her political commitment began on the streets of Toxteth, Liverpool, in the 1980s. Photograph: Bundu press office

An ex-DJ and activist for Oxfam, Bundu is poised as Salvini’s nemesis. The interior minister has closed Italian ports to NGOs that rescue migrants, and he was recently one of the speakers at the controversial Family Congress in Verona, which brought together anti-gay, anti-feminist and anti-abortion activists from around the world.

Bundu is running for office in a country that in recent years has sunk into a climate of intolerance, and where thousands of Italians have joined self-described fascist groups, more than 70 years after Benito Mussolini’s death. Her political rival, Ubaldo Bocci, who is running under the League and Brothers of Italy parties, has decided to abandon the upcoming 25 April holiday, which celebrates the country’s liberation from the Nazis.

Politics is riding a wave of hatred that gets more threatening and unruly every day

The vote is seen as a three-way contest between Bundu, Bocci and the faltering centre-left Democratic party (PD), out of the eight candidates standing. But if Bundu makes it through to a second-round runoff, she can expect support from former PD voters.

“Politics is riding a wave of hatred that gets more threatening and unruly every day,” said Bundu. “I too have been a victim of Italian racial hatred. When I opened my door to the parcel delivery man, he asked me if the owner was home, thinking that I was the cleaning woman. While taking a stroll with my daughter, a woman once called me a ‘dirty nigger’. I sued her, and she was found guilty of racial hatred. What’s worse is that people who insult blacks or beat Africans do so without fear of reprisal, legitimised by the pronouncements of political leaders and a subsequent perception of impunity.”

Bundu’s passion for politics did not emerge on the stage of the Alfieri Theatre. Her political commitment began on the streets of Toxteth, Liverpool, in the 1980s.

“I was studying black history in the city’s libraries and participated actively in the neighbourhood’s protests,” she says, describing a “politically charged city” still reeling from the riots earlier in the decade, during which homes were torched and many people were hurt.

Following the announcement of her candidacy, some people in Florence turned up their noses, and argued that her entry into politics – in a country that reluctantly accepts black footballers on its national team – could be counterproductive to the left and help hand victory to the extreme right. For some, a black woman candidate in Florence could be interpreted as provocation in an Italy dominated by Salvini.

“The real provocation is not that I am a woman, or even a black woman. The real irritation for some is that we have succeeded in creating a coalition of parties of the true left, whose values are anti-fascism and the struggle for freedom,” said Bundu.

“We represent the left of equality, the left that is close to the people, the left that Italy has always had within itself, but that recently seems forgotten. Florence is the city that received the gold medal for its resistance against the fascists. The time has come to remind people.”

• This article was amended on 23 April 2019. Quotes from Bundu about her time in Liverpool were edited to clarify that she studied in the city in the late 1980s and not during the Toxteth riots earlier in the decade.