Paul-Emile Brandt was born on 12 January 1880, the eldest son of Louis-Paul Brandt, who with his brother César had turned the family watch business into Omega in Biel/Bienne. He was working in New York when his father died in April 1903; aged 23, he was called home to run the factory with his uncle, and when César also died that year, responsibility for Omega fell on him, his brother Adrien and his cousins Gustave and Ernest. He completed his father's plan to turn the firm into a public limited company.
He believed the industry needed consolidation. After the losses that followed the First World War he worked from 1925 towards a union with Tissot of Le Locle, and in 1930 the two firms merged in the Geneva holding company SSIH (Société Suisse pour l'Industrie Horlogère); the agreement gave Omega the top of the market and Tissot the middle. Lemania, the Vallée de Joux maker of complications and chronograph movements, joined soon after, allowing Omega to time the 1932 Los Angeles Olympics. The group went on to absorb or create some fifty companies, and Omega launched the Seamaster in 1948 and the Constellation in 1952.
At the factory he concentrated on production and the large workforce, and promoted a staff pension fund that was widely copied in the industry; he was known as a demanding and gruff manager. He founded and presided over the Bernese cantonal association of watch manufacturers through the inter-war crises, joined the Swiss Chamber of Watchmaking in 1922 and became its vice-president, and sat on the local committee of the Swiss National Bank.
His date of death is given as 25 August 1954 by the Grail Watch Wiki, while Omega's history and Wikipedia have Joseph Reiser taking over in 1955 and Casadi's tenure ends in 1955. The start of the Tissot talks is given as 1925 by Wikipedia and 1928 by the Grail Watch Wiki.