Charles-César Brandt was born on 28 April 1858, the younger son of Louis Brandt, founder of the La Chaux-de-Fonds watch business that became Omega. Like his brother Louis-Paul he went to school in La Chaux-de-Fonds and learned the watch trade, and he was then sent to England to learn the language and the international watch business. On 1 July 1877 the brothers joined their father, and the firm became Louis Brandt et Fils.
When their father died in 1879, César was 21. The brothers moved the business to Biel/Bienne in 1879 to 1880 to manufacture watches industrially, and César became its traveller and salesman while Louis-Paul ran production. He made his first business trip to Brazil in 1885, and his travels led to the opening of a Paris branch in 1889; he settled in Paris, which became the firm's main sales office outside Switzerland.
The brothers' 19-ligne Omega calibre of 1894, built with interchangeable parts, made Louis Brandt et Frère the largest watch factory in Switzerland, with about 800 staff by 1896, and gave the company the name it took in 1903. When Louis-Paul fell ill, César also took on manufacturing and personnel. Louis-Paul died in April 1903; César fell ill that September and died later in the year, aged 45, leaving the business, then making 240,000 watches a year, to four young heirs: his sons Gustave and Ernest and his nephews Paul-Emile and Adrien.
His date of death is given as 11 October 1903 on his Grail Watch Wiki page and as November 1903 on his brother's; Omega gives only the year. His career details come mainly from that enthusiast wiki.