Joshua Spencer, who was expelled from the Conservative Party over the incident, admitted sending the message about the Commons home affairs committee chair on April 11.
Leeds Magistrates Court heard the 25 year-old, from Knottingley, West Yorkshire, sent a message to someone he met on a dating site, suggesting Cooper should “pay” for trying to stop a no-deal Brexit and he would have a “crack head” see she was “beat up”.
It reads: “I’m already organising her to her hurt. Amazing what crack heads will do for £100. I’m gonna get her beat up.”
Spencer was sentenced to nine weeks in prison.
Tory MP Andrea Jenkyns gave evidence to the court, providing a character reference for Spencer, according to the Guardian.
Jenkyns, who defeated Cooper’s husband, Ed Balls, in Morley and Outwood constituency in 2015, gave a statement.
In it, she said Spencer was “a decent and honest person whose heart is in the right place and who always helps people in need”. She said she did not condone what he had done but claimed he had been “let down by the system” and desperately needed help for his mental health problems, including biopolar disorder and suicidal thoughts.
Cooper is the MP for Normanton, Pontefract and Castleford in West Yorkshire.
The court heard that as well as attending the count in Cooper’s constituency, Spencer was at the “big Brexit bash” party organised by Jenkyns in Morley last week.
But he has since been kicked out of the party and the Tories say he was suspended when the allegations came to light.
A Conservative Party spokesperson said: “This kind of conduct has no place in our public life and we extend our sympathies to Yvette Cooper for the distress and harm this incident must have caused.
“Mr. Spencer has been expelled from the party, following his suspension from the party when he was charged in court for these offences.”
In a victim statement to the court, Cooper said: “Disagreement and debate are a healthy part of our politics. But violent threats, intimidation and abuse, online or offline, undermine our democracy.
“MPs across the country, particularly women MPs, have unfortunately become accustomed to a continued stream of abuse online and threats from a small number of people, often on the extreme fringes of politics. But this behaviour is not normal, and we must never treat it as so.”
She added she decided to take action as the threats grew “more serious”.
“In this case the individual lives in my constituency, has contacted me directly on a regular basis, is an active member of the local Conservative party and prominent in mainstream local politics in my constituency,” she said. “I understand he denied responsibility for some considerable time and I am still not aware of any expression of remorse or regret.
″During the period in which the police were investigating he also continued to contact me and organised a hostile event outside my constituency office. Given the nature of the Facebook message and his continued behaviour, I and my office have had to take the threat very seriously.”
Following criticism over her intervention, Jenkyns defended giving evidence, saying: “I have known Joshua for a number of years. I stand by my decision to have given him a personal reference.
“Josh has bipolar and had mental health issues since his father’s suicide in 2015 and I was, and remain, concerned about his emotional and mental well-being and wanted to make absolutely sure it was taken into consideration as part of the judicial process.
“I will be seeking assurances that he will get the support he clearly needs as part of his rehabilitation.”