Guillaume Lasceux (3 February 1740 - 1831) was a French organist, improviser and composer.
Born in Poissy, Lasceux began his career as an organist in the parish of St-Martin of Chevreuse in 1758. He moved to Paris in 1762 to study music composition for five years with Charles Noblet, organist and harpsichordist of the Opera. He succeeded him to the Mathurins in 1769. In the same year, he was appointed organist at St-Aure, and 10 years later, at the Minimes convent, Place Royale [fr], with similar posts at the College of Navarre and the Magloire Seminary [fr].
In 1769, he replaced Claude-Nicolas Ingrain on the organ of the Saint-Étienne-du-Mont church, of which he officially became titular in 1774. During the Revolution, he lost most of his posts and had to earn a living by accompanying the theophilantropic ceremonies in Saint-Étienne-du-Mont, converted into a "Temple of Branch piety". He resumed his organist's post in 1803, after the restoration of Catholic worship there, and retired on 2 January 1819.
Recognized as a virtuoso on the organ, harpsichord or forte-piano, Lasceux became famous for his improvisations inspired by the Last Judgement.
His work includes vocal pieces, chamber music and numerous organ pieces.
