Early life
In 1779 he organized, and made himself head of, the Protestant associations, formed to secure the repeal of the Catholic Relief Act of 1778. On 2 June 1780 he headed a mob that marched in procession from St George's Fields to the Houses of Parliament in order to present a huge petition against Emancipation. After the mob reached Westminster the "Gordon Riots" began. Initially, the mob dispersed after threatening to force their way into the House of Commons, but reassembled soon afterwards and, over several days, destroyed several Roman Catholic chapels, pillaged the private dwellings of Catholics, set fire to Newgate Prison, broke open all the other prisons, and attacked the Bank of England and several other public buildings. The army was finally brought in to quell the unrest and killed or wounded around 450 people before they finally restored order. For his role in instigating the riots, Lord Gordon was charged with high treason. However, thanks to a defense by Baron Erskine, he was acquitted on the grounds that he had no treasonable intent.

The "Gordon Riots"
In 1786 he was excommunicated by the archbishop of Canterbury for refusing to bear witness in an ecclesiastical suit; and in 1787 he was convicted of defaming Marie Antoinette, the French ambassador and the administration of justice in England. He was, however, permitted to withdraw from the court without bail, and made his escape to the Netherlands. On account of representations from the court of Versailles he was commanded to quit that country, and, returning to England, was apprehended, and in January 1788 was sentenced to five years imprisonment in Newgate.

Conversion to Judaism
On the 28th of January, 1793, Lord George Gordon's sentence expired and he had to appear to give claim to his future good behaviour. When appearing in court he was ordered to remove his hat, which he refused to do. The hat was then taken from him by force, but he covered his head with a night cap and bound it with a handkerchief. He defended his behaviour concerning his kippah by quoting the Bible "in support of the propriety of the creature having his head covered in reverence to the Creator." Before the court, he read a written statement in which he claimed that "he had been imprisoned for five years among murderers, thieves, etc., and that all the consolation he had arose from his trust in God."
Since he had brought as guarantors two Jews, whom the court would not accept as witnesses, Gordon was again remanded to his prison cell. Although his brothers; the 4th Duke of Gordon and Lord William, the future Vice-Admiral; and his sister, Lady Susan; offered to cover his bail; Gordon refused their help saying that to "sue for pardon was a confession of guilt."
In October of the same year Gordon caught the typhoid fever that had been raging in Newgate throughout 1793. Christopher Hibbert, another biographer, writes that scores of prisoners waited outside his door for news of about his health; friends, regardless of the risk of infection, stood whispering in the room and praying for his recovery - but George Gordon died on November 1, 1793 at the age of 42.
A serious defence is undertaken in The Life of Lord George Gordon, with a Philosophical Review of his Political Conduct, by Robert Watson, M.D. (London, 1795). The best accounts of Lord George Gordon are to be found in the Annual Registers from 1780 to the year of his death. He figured as a character in Charles Dickens' historical novel Barnaby Rudge.