Louis-Paul Brandt was born on 8 February 1854, the elder son of Louis Brandt, who had founded a watch-assembling business in La Chaux-de-Fonds in 1848, buying parts from local craftsmen and selling the finished pocket watches across Europe, with England as his main market. He was schooled in La Chaux-de-Fonds and learned the watch trade, and on 1 July 1877 he and his brother César joined their father, the firm becoming Louis Brandt et Fils.
Their father died in 1879, and the brothers decided to industrialise along American lines. They set up in Biel/Bienne, moving the company there in 1880, and launched their first machine-made calibre that year; by the end of the decade the firm was the largest in Swiss watchmaking. Their factory complex in Bienne, the Gurzelen works, also housed La Générale, which made cheaper watches under the Helvetia name, and they founded the case maker La Centrale to supply the group. In the division of work, Louis-Paul oversaw manufacturing and the workforce, while César travelled and handled clients.
In 1894 the brothers launched the 19-ligne Omega calibre, made with interchangeable parts under full in-house control. It was so successful that in 1903 the company took the name Louis Brandt et Frère, Omega Watch Co., and by then it employed about 800 people making 240,000 watches a year. Louis-Paul fell ill in the early 1900s and died on 14 April 1903; his obituary blamed "excessive work". César died months later, and the firm passed to Louis-Paul's sons Paul-Emile and Adrien and César's son Gustave. He had long declined invitations to join the cantonal parliament and town authorities, accepting only late in life.
Details of his division of work, his obituary and his civic roles come from the Grail Watch Wiki, a secondary enthusiast source.