Actor Adam Deacon, who is from Bethnal Green, has been given a restraining order after "trolling" his former mentor and Adulthood director Noel Clarke on Twitter.
Deacon, 32, subjected Clarke to a "barrage" of abusive messages after a row over the title of hit film Anuvahood.
He branded Clarke a "bully" and accused him of sabotaging his career in hundreds of "consistent and continuous" posts on Instagram and Twitter.
Once good friends, the pair stopped talking after the dispute over the 2011 film, in which Deacon made his directorial debut and won a Bafta.
Clarke previously told the court that he helped launch Deacon's career by selecting him to star in his films Kidulthood and Adulthood.
A restraining order barring Deacon from contacting Clarke in any way, including on social media, was imposed along with a conditional discharge at Hammersmith Magistrates' Court.
Oscar Merry, defending, said in mitigation that Deacon, who is unemployed, has a "history of mental health difficulties".
"There was plainly a long-running feud between Mr Deacon and Mr Clarke dating back to 2010 at the very least," he added.
"Perhaps Mr Deacon had justifiable reasons for feeling aggrieved towards Mr Clarke, perhaps he did not.
"What is clear is that his online trolling of Mr Clarke overstepped the mark from unreasonable behaviour to actions that were unacceptable."
He described Deacon as a "decent and kind human being" and said his behaviour was "totally out of character".
Mr Merry added that Deacon was "profoundly ill", suffering from depression and having a "full mental breakdown" at the time of his offending.
"He increased his use of skunk cannabis as a form of self medication," he said.
Deacon was sectioned under the Mental Health Act in January 2015 and has been diagnosed with bipolar disorder, the court was told.
District Judge Shenagh Bayne previously said Deacon had made "veiled threats" by posting pictures of Clarke's family and had a "grievance that goes back a long time".
"The sheer number of messages that you sent is indicative of your intention to harass Mr Clarke," she added.
"You were aware of the effect that your behaviour would have.
"You clearly were trying to elicit a response from Mr Clarke otherwise why post #wallofsilence, #industry and #standuptobullies."
Clarke, who starred in Doctor Who, said he was so worried about the content of the messages Deacon posted that he informed his children's school, which subsequently changed security codes around the building.
"You just don't know what is going to happen," he said.
Even after Clarke went to the police in November 2014, Deacon continued to post abuse, calling his fellow star a "snitch".
Deacon is best known for playing the main character, Jay, in the films Kidulthood and Adulthood, which saw him appearing alongside Clarke.
Giving evidence, Deacon claimed he had not harassed Clarke, who seemed to "have it in" for him from the beginning.
"He would bully and belittle me on set in front of people - it would be a constant thing," the actor said.
He told the court he was only paid around £1,500 for his role in Kidulthood, despite being told by Clarke that he would "make a lot more".
However, the actor admitted posting some messages on Twitter making reference to bullying, but insisted these were not directed at Clarke.
"I didn't '@' him, I didn't mention him. That's why I'm so confused as to why there's a harassment charge," he said.
Deacon, who is also a rapper and played firearms officer Robbie in Channel 4 police drama Babylon, which aired last year, appeared in court wearing a pastel pink shirt and grey suit.
Judge Bayne described Deacon's behaviour as "concerning" but said it was an "isolated incident which was occasioned by a breakdown in your mental health".
"I deal with this in the context of the state of your mental health at the time," she added.
"You clearly have got an underlying issue which was exacerbated by your use of a mind altering substance, cannabis."
She said the abuse had an "appalling" effect on Clarke and added that he was "visibly distressed" when he gave evidence during the trial.
"He was harassed and then put through the ordeal of giving evidence at court, he had to come and go through all of the matter here in front of me.
"It is not acceptable to just post things out there and think it doesn't constitute any kind of threat to somebody," she added.
Judge Bayne told Deacon he had provided "powerful" references and added that it was "quite significant" he is volunteering as a mentor for people with mental health problems.
The restraining order and conditional discharge will both last for two years.
Earning some €1.5million last year thanks to a string of sell-out stand-up tours, hosting duties on Sky’s sports panel series, A League of Their Own and a starring role in Channel 4’s campus comedy Fresh Meat, Jack Whitehall is in a rather fortuitous situation at only 27 year-old.