Judge Richard Spearman said Craig Kline had subjected Glenn to a “prolonged” online attack.
The judge said Glenn had sued over a “long series of publications”, mainly Twitter posts, between November 2018 and June 2020.
He heard that Glenn had been accused of corruption and covering up child sexual abuse.
Judge Spearman, who is based in London, delivered a ruling on Friday after hearings in the High Court.
He heard that the allegations had prompted the FA to launch an inquiry. Investigators found no evidence of any wrongdoing and said Kline had produced no evidence to support his allegations.
A judge had ruled, at an earlier hearing, that Glenn had been libelled and harassed, after Kline failed to file a defence.
Judge Spearman considered arguments about damages at a hearing in February and delivered his ruling on Friday.
Glenn, FA chief executive between March 2015 and August 2019, had told the February hearing that the allegation that he was “complicit in child abuse” was “absolutely terrible” because he was “responsible for the safeguarding of children”.
The judge said Kline was assistant director of football and director of statistical research at Fulham between 2014 and 2017. Glenn said he had never worked with, met or had any dealings with Kline. He said he knew of “no reason for personal animosity” towards him which might explain Kline’s actions.
“The defendant subjected the claimant to a prolonged attack over several months,” said Judge Spearman.
“The allegations were very serious, and went to the core elements of the claimant’s life.
“They threatened, and indeed may be said to have been designed to threaten, the claimant’s livelihood and professional standing; and they resulted not only in an in-depth investigation at the FA but also a continuing need for the claimant to allay the concerns of organisations where he held office.
“It was particularly hurtful and distressing that the claimant was accused, entirely without foundation, of being complicit in covering up child abuse when, in truth, he was concerned to ensure that the FA took safeguarding very seriously.”
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