Westminster Magistrates Court was told Amy Dalla Mura, 56, targeted Anna Soubry between January and March, on one occasion forcing her to abandon a public speaking engagement.
Mura is standing for the far-right English Democrats against Soubry, a former Conservative MP who is seeking re-election as an independent in the Broxtowe constituency in central England.
Chief magistrate Emma Arbuthnot described the defendant's behaviour as "oppressive and unacceptable", assessing that she was "driven by anger at Ms Soubry's political views on Brexit".
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She said she was satisfied with Mura's verbal abuse, including one occasion when she called Soubry a traitor as she was giving a television interview inside parliament, was harassment.
The judge granted Mura bail pending the completion of psychiatric reports and ordered her to reappear for sentencing on December 16 - four days after the general election.
As a condition of her bail, the judge banned her from campaigning in person in Broxtowe and ordered her not to mention Soubry by name as she canvassed for votes.
Last week, a man who sent a death threat to Soubry was jailed for one year after warning Soubry she would suffer the same fate as Jo Cox, an opposition Labour party lawmaker who was murdered by a neo-Nazi days before the 2016 EU referendum.
More than three years on, and with parliament yet to fully endorse Prime Minister Boris Johnson's exit terms, opinion has polarised, with MPs facing a barrage of abuse.
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A police unit set up after Cox's murder said it was probing increasing levels of abuse, threats and intimidation against MPs, their staff or families.
Safety warnings for the campaign have been issued to candidates.
Adrian Usher, of the Metropolitan Police's Parliamentary Liaison and Investigation Team, arrested and charged Mura, who pleaded not guilty.
He said: "Strong political opinions are no excuse for abuse, harassment or intimidation of members of the public or parliamentarians.
"Police will treat such allegations seriously and seek to bring offenders to justice - as today's conviction demonstrates."
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