Police have arrested a 25-year-old man on suspicion of harassment after Twitter abuse was aimed at feminist campaigner Caroline Criado Perez and Walthamstow MP Stella Creasy.
Both women have complained about being sent vicious tweets on the site in the past week.
A Scotland Yard spokesman said: "Today, 30 July, Northumbria Police arrested a 25-year-old man on suspicion of harassment.
"This arrest will form part of two ongoing MPS investigations relating to allegations made to police by two separate victims, who made reports of malicious communication to police on 25 and 29 July."
Ms Criado Perez, 29, has said Twitter needs to "get a grip" on security, as it emerged bosses were likely to face a grilling from MPs.
She said the social network was ill-equipped to handle episodes of sustained abuse and needed to work more closely with police to deal with internet trolls.
Ms Criado Perez met Twitter directors on Monday night along with Ms Creasy, who received a similar torrent of abusive messages after she offered support to the freelance journalist.
"This will have been a wake-up call for Twitter," Ms Criado Perez said.
"It will hopefully have led them to realise that they are not equipped to deal with this kind of thing properly.
"They need to get a grip and figure it out."
The campaigner, who received assurances that Twitter is working to improve its procedures for reporting menacing behaviour, said the police also needed to "step up".
"We had a positive conversation about making reporting quicker, simpler and more focused on getting results for the victim," she added.
"I feel that finally they're taking this issue seriously, though it's a shame it's taken this worldwide outcry for them to act.
"We'll be keeping up the pressure in the coming weeks, but the signs of some serious, positive changes are good."
Twitter bosses look set to face questions from MPs when the Culture, Media and Sport Committee examines issues surrounding child protection in the Autumn.
Committee chair John Whittingdale said: "I would have thought it very possible that the committee might want, in the course of our inquiry, to talk to Twitter."
He added: "It isn't that the law needs to be changed; the question is how you identify people and how you prevent them (from abusing others online).
"That is the big question and it is one we would wish to explore with internet companies to determine whether they are doing as much as they can or whether they should do more. I think that's a very live issue."
Ms Criado Perez, from north London, found herself at the centre of a public furore after she launched a campaigned to have a woman's picture printed on a new banknote.
This led to the announcement that Jane Austen would feature on the new £10 note from 2017 but also drew her a litany of depraved messages from social networkers.
Ms Creasy was sent similarly vicious tweets when she spoke out in support of the campaigner.
Ms Criado Perez said the online attack left her feeling "under siege" and terrified in her own home.
"It's been exhausting and I think it has had an impact on my mental heath, having all that hate directed at me," she said.
"While I'm not walking around in constant fear, it is all bubbling under the surface."
Officers have also questioned and bailed a 21-year-old man in connection with the messages sent to Ms Criado Perez.
Twitter said it was in contact with the police over the abusive tirades.
A spokesman said: "We value the feedback from our users and are testing ways of simplifying the reporting process, including a broad roll out of in-Tweet reporting beyond the current availability on the iPhone app and mobile web.
"We have processes in place for working with law enforcement and are currently in communication with the police, as well as the affected parties."
The social network has announced plans to include a button for reporting abuse within every tweet - something which is already available on its iPhone app.
But critics argue this does not go far enough and only directs users to the existing reporting form which, they claim, is too long and impractical.
A change.org petition calling for Twitter to beef up its reporting procedures had drawn more than 90,000 signatures by this evening.
The uproar has also prompted Tory MP Claire Perry - who has been advising the Prime Minister on measures to tackle the spread of extreme pornography and child abuse online - to reveal the extent of the abuse she too has received on Twitter.
The Devizes MP wrote: "I am tempted to shut down my Twitter account given the trolling going on incl. to me - but that would be giving in."