At least three eggs were hurled at the high-profile champion of Muslim women's rights, one of which broke on her face, soiling her hair and jacket.
Gavin Reid 23, ran away after shouting the abuse and throwing the egg but was identified from photos and BBC footage
At the time of the attack last November, Baroness Warsi - now chairman of the Conservative Party and one of David Cameron's rising stars - was on a visit to Luton with a Tory election candidate.
The group of ten protesters shouted abuse in English and Urdu at the Dewsbury-born former solicitor, accusing her of not being a proper Muslim and supporting the deaths of civilians in Afghanistan. They also demanded the introduction of Sharia law, the Islamic code of conduct, in Britain.
Former removals man Reid, of Luton, was found guilty of an offence under the Public Order Act yesterday at City of Westminster Magistrates Court in London.
Sentencing, District Judge Elizabeth-Roscoe said: 'Throwing eggs goes beyond legitimate political protest and is quite clearly disorderly behaviour, and it is also threatening, abusive and insulting behaviour.'
It is thought Reid is of Jamaican origin and converted to Islam two years ago while serving a 42-month prison sentence for GBH.
Last night Sayful Islam, who was at the protest in Luton last November and is a spokesman for Islam4UK - the group led by so-called hate preacher Anjem Choudary - admitted he knew Reid.
But he claimed Reid was not a member of Islam4UK and denied that the group members had shouted the abuse.
The court heard that Reid was identified as the egg-thrower from BBC footage despite his face being hidden by his jacket hood. He was arrested 15 days later and gave a 'no comment' interview to police.
He later conceded that he threw an egg at the peer but he denied the charge against him.
James Walker, representing Reid, argued that to be found guilty, prosecutors had to prove his actions had caused 'harassment, alarm or distress'.
Baroness Warsi, 39, the first female Muslim Cabinet minister, did not give evidence in the trial. Mr Walker said she 'might not have been in the same league as John Prescott' who infamously gave a right hook to an egg-thrower, but he described her as 'no shrinking violet'.
The judge said she could not be sure that the peer 'felt any harassment, alarm or distress'.
However, she concluded Reid's actions did meet the criteria for conviction as they had irritated and angered Baroness Warsi's companions.
The judge said Reid had already served the sentence during his time on remand since May.