Louis Perrin PC (15 February 1782 – 7 December 1864) was an Irish barrister, politician and judge.
Perrin was born in Waterford, the son of Jean Baptiste Perrin (fl. 1786). Jean Baptiste, a Frenchman, had come to Ireland to seek a living: he set himself up as a teacher of French, and earned his living mainly as a private tutor to wealthy Irish families.
Louis Perrin was educated at the diocesan school at Armagh. Removing to Trinity College, Dublin, he gained a scholarship there in 1799, and graduated B.A. in 1801. At the trial of his fellow-student, Robert Emmet, in 1803, when sentence of death was pronounced, Perrin rushed forward in the court and warmly embraced the prisoner. He devoted himself with great energy to the study of mercantile law; in Hilary term 1806 was called to the bar, and was soon much employed in cases where penalties for breaches of the revenue laws were sought to be enforced. When Watty Cox, the proprietor and publisher of 'Cox's Magazine,' was prosecuted by the government for a libel in 1811, O'Connell, Burke, Bethel, and Perrin were employed for the defence; but the case was practically conducted by the junior, who showed marked ability in the matter. He was also junior counsel, in 1811, in the prosecution of Sheridan, Kirwan, and the catholic delegates for violating the Convention Act. In 1832 he became a bencher of King's Inns, Dublin.
He was a Whig in politics, supported Catholic Emancipation, and acquired the sobriquet of 'Honest Louis Perrin.' On 6 May 1831, in conjunction with Sir Robert Harty, he was elected as Member of Parliament (MP) for Dublin City. Being unseated in August, he was returned to the House of Commons for Monaghan at the general election on 24 December 1832, displacing Henry Robert Westenra, the previous Tory member. At the next general election, in 1835, he came in for the city of Cashel, on 14 January 1835, but resigned in the following August, to take his seat on the bench. In the House of Commons he strove to prevent grand jury jobbery, and made an able speech on introducing the Irish municipal reform bill; and he was untiring in his efforts to check intemperance by advocating regulations closing public houses at eleven o'clock at night.