Shortly after the May 2010 general election, Stella Creasy was walking into a lift at the Houses of Parliament when she was stopped by a male Conservative politician and told that it was reserved for the use of MPs only. Creasy had just been elected to represent Walthamstow with a majority of more than 9,000.

It not likely that he or any of his colleagues could make the same mistake today. After three years in Westminster, Creasy might be considered to have made one of the most striking and effective parliamentary debuts in recent times, thanks to outspoken interventions around sex education and violence against women, and an almost single-handed campaign against payday lenders that was credited with forcing the Treasury to tighten restrictions on the practice late last year.

But it may be the unwelcome events of the past week which have seen the MP make the biggest impact outside the Westminster village, after she spoke out in support of the journalist Caroline Criado-Perez, who had received a barrage of violently misogynist messages on Twitter and elsewhere as a result of campaigning for a woman to feature on Bank of England notes.

Creasy was soon the recipient of a similar wave of rape and death threats, but, like Criado-Perez, was not a woman to back down. The MP declared herself unintimidated by the "morons", went straight to the police to report her abusers, and took the fight to Twitter, declaring herself "frankly incandescent" at the company's response to the treatment she, Criado-Perez and others, including the Tory MP Claire Perry, had received.

She also found time for a barnstorming appearance on Newsnight, declaring: "What we mustn't do is make the mistake of thinking that because this is happening online it is somehow less serious," and berating rightwing commentator Toby Young for a tweet he had sent about an MP's "tits". Twitter has now agreed to include harassment in the definition of behaviour it considers abuse, and has confirmed plans to introduce a button on all platforms allowing users to report abusive comments.

It is not a surprise to those who have known and worked with Creasy in the past. Edward Andersson, deputy director of Involve, a thinktank focusing on public participation in politics where Creasy worked in the late noughties, describes her as "a good listener. She's very attentive, very personable, but also … Well let's just say, I don't envy the people who are harassing her. Stella is incredibly principled and won't back down from her beliefs. She's a formidable person in many ways."

Creasy was spotted as a rising star soon after her entry to Westminster – and not only by those on her own side. While LabourList selected her as its MP of the year last year for her work on payday loans, recognition has come also from the Spectator, which named Creasy campaigner of the year in 2011, the magazine calling her "an example of how to do opposition politics".

Similarly, the influential Tory website ConservativeHome has called her "Labour's most interesting member of parliament", less for her wide outside interests than for speaking what it called "no end of good sense" on public spending and the national debt. As "one of the few genuine Labour stars of the 2010 intake", the website concluded, Conservatives would be wise to be wary of such a skilled political operator.

"The thing about Stella is that she managed to be incredibly strong while remaining human," says her friend Liz Kendall, who was elected Labour MP for Leicester West in the same parliamentary intake.

"She has tried to work across the political parties ... but she's also approachable personally and very normal, and that means she speaks to people about things that they relate to."

But effective single-issue politicians do not always make the most comfortable team players, and there was some initial caution inside Labour, according to insiders, about whether Creasy might be too wedded to her own campaigns to dedicate herself to a ministerial brief. More than a third of Labour's new 2010 MPs were given shadow ministerial roles by Ed Miliband only months after the election, but, unlike colleagues Rachel Reeves, Jonathan Reynolds, Luciana Berger and others, Creasy had to wait another year before being promoted; she is now shadow minister for crime prevention in Labour's home affairs team under Yvette Cooper.

The daughter of a teacher mother and opera singer father, Creasy spent her early years in Manchester before the family moved to Colchester, where she attended a girls' grammar school (having failed the 11-plus and only been given a second chance because the family moved south, she is opposed to selection). After a degree in social sciences at Cambridge she completed a PhD entitled "Understanding the Lifeworld of Social Exclusion" at the LSE (allowing her to respond to one Twitter troll with: "That's dumb Dr blonde bitch to you, actually").

Thirteen years ago she moved to Walthamstow in north-east London, where she became a councillor and has served as deputy mayor, chief whip and mayor of Waltham Forest council. She has also been a speechwriter and researcher for a number of senior politicians including Douglas Alexander and Charles Clarke, and worked for the public participation campaign group Involve and the Scout Association before becoming an MP. She has a long-term partner with whom she lives in Walthamstow.

But Creasy also has hinterland outside politics, most notably a love of indie music, particularly the Leeds band the Wedding Present, for whose latest album she wrote sleeve notes about "the burning confusion of rejection" and "the way in which heartache eats you up inside".

Andersson says that while Creasy's ambition to become an MP was always clear, "everything she has done was always very local, very focused on Walthamstow. I'm convinced that if she had not been selected she would still have been there working for the community."

Kendall says: "What was interesting about the payday loans campaign was that she took a real issue from her constituency that she had seen and experienced, and gave a voice to something that was already happening. That's one of the reasons it had such cut-through and why she has been so effective."

Creasy has said that every time she visits a high street, she stops and counts the pawnshops and lenders, to check how their numbers have grown. In a YouGov poll published on Thursday, 89% of Britons said they believed payday lenders "take advantage of the vulnerable", showing the degree to which awareness has grown on what was once a relatively marginal issue.

Criado-Perez first contacted Creasy to ask if she would support the banknote campaign having observed, she says, "how she stands up for women again and again". They brainstormed ideas how the MP could help – she organised a letter of 46 MPs to David Cameron in support of the campaign – and when the threats began in response to the campaign, Criado-Perez contacted Creasy again: "I thought she would know what I should do about it and would be able to advise me really well."

Since then, Creasy has been "incredible", Criado-Perez says. "Checking in on me, taking on the role of mother really, and telling me off for not eating enough. It's been quite hard to find time to eat, and you know that eating can be quite difficult if you are stressed."

The wave of hostile messages to Creasy's Twitter site has barely abated, and on Thursday she continued to rebuff some, engage wittily with others, and encourage those with information about the most serious threats to go to the police.

But misogynist abuse aside, the business of local and national politics goes on: on Thursday that included liaising with constituents about the recent rape of a 12-year-old girl in the borough, and with immigration officials over an early morning raid at the local tube station. She also wrote to home secretary Theresa May in her role as shadow home office minister about the DNA records of suspected criminals.

But it's not all politics. "In light of all the troll comments have been sharing," Creasy tweeted, "think only fair I share these cute dogs."

She added the hashtag #whattwitterreallyfor.