Initiated into geometry by Evangelista Torricelli (1608-1647), Segni became secretary to Prince Leopold de' Medici, for whom he undertook various diplomatic missions in Europe. He also served as secretary of the Accademia della Crusca. Lastly, he was the Accademia del Cimento's first secretary until May 20, 1660, when he was replaced by Lorenzo Magalotti (1637-1712).