The charismatic 36-year-old has in recent years been one of the fiercest critics of the secessionist project in media interviews and during debates in Catalonia's regional parliament.
She has blasted the separatists' bid to break Catalonia away from Spain as a "coup against democracy" and accused the region's axed president, Carles Puigdemont, of having embarked on a "Kafkian" process and of not listening to opponents.
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"You don't like to show your face, you don't like to talk, you don't like to debate, you don't like to negotiate with anyone who is not like you," she said during a debate in the Catalan parliament just before it voted to declare independence in October.
Born in Jerez de la Frontera in the southern province of Cadiz, Arrimadas has a degree in law and business administration. The youngest of five children, she moved to Catalonia more than a decade ago to work as a lawyer in the private sector.
Her life changed in 2010 after she attended a rally of centrist party Ciudadanos, founded just four years earlier to fight Catalan nationalism and corruption.
She joined the party the following year and quickly rose through its ranks. As the leader of the opposition in the Catalan parliament since 2015, Arrimadas -- who is fluent in Catalan and speaks English and French and
describes herself as shy -- has shown her knack for communication.
She has branded her rivals' secessionist rhetoric as "monothematic" and their nationalism "exclusive".
Her quick reflexes were on show during her final rally before the election in Nou Barris, a working class Barcelona neighbourhood.
As she started to speak, people further away started banging pans in protest against Ciudadanos.
"There are others who don't want us to talk but we are going to talk loudly at the ballot box," she said to cheers and shouts of "presidenta, presidenta!".
Married to a Catalan former politician from the separatist camp, Xavier Cima, Arrimadas presents herself as representative of all Catalans -- including those like herself who migrated to the wealthy region from other parts of Spain in search of a brighter future.
On election night with party leader Albert Rivera. Photo: AFP
Arrimadas's Ciudadanos won more than a million votes in Thursday's poll, its best ever result.
The party came out on top in terms of vote count, but was defeated in terms of seats by the three separatist lists.
Still, Arrimadas celebrated the result not just for her party, but for the anti-independence camp.
"The nationalists will never again be able to speak in the name of all Catalonia. We are all Catalonia," she said in a speech to supporters after the result was announced.
Britain's The Guardian newspaper likens Arrimadas to French President Emmanuel Macron for successfully carving out a centrist path in a country long dominated by bipartisan politics.
Former French prime minister Manuel Valls, who was born in Barcelona and has taken an active role in the campaign against Catalan separatism, has said he "admires" her speeches.
But her fierce defence of Spanish unity has also won her many detractors. The former speaker of the Catalan parliament, Nuria de Gispert, once said Arrimadas should return to Cadiz.
A popular comedy programme on the Catalan public television network, Polonia, has portrayed her as a photogenic but vacuous Barbie doll, the "perfect candidate" that spews out anti-separatist slogans.
"I receive daily the most spectacular hate and affection, in equal parts," Arrimadas said during an interview with private television Telecinco last month.
She has been a supporter of FC Barcelona, a symbol of Catalan culture, since she was a teenager and would cover her binders in high school with pictures of the club's former star player and coach Pep Guardiola, a fierce defender of independence.
Andres Rodriguez Benot, who teaches international law at the Pablo de Olavide University in Seville, remembers her as a "brilliant" yet "reserved" student there.
He said when a group of students falsely accused her of forging language certificates in order to obtain a scholarship, Arrimadas reported the incident, and the university sanctioned the guilty students.
"She is a rigorous person who respects legality," he said. "With her, you can forget about the word corruption."