Souillot was born in Dijon in 1967 as the son of a gas-worker.[1] He described his parents as "not revolutionary" however they were "committed against social inequalities". At the age of 16, he obtained a pastry-confectioner and chocolate-ice cream maker diploma. In 1994, he was hired as a specialist in the maintenance and installation of service stations at Schlumberger (now Tokheim), and in 1995 he joined the Workers' Force.[1]
In 2008, he joined FO Metals and became General Secretary in charge of steel and base metals workers.[1]
In 2015, he was appointed as the Confederal Secretary of the Workers' Force.[1] On 3 June 2022, during the 25th Congress of the Workers' Force in Rouen, he was voted as the General Secretary of the Workers' Force.[1]
He opposes the 2023 French pension reform law and, after his election, said that he wished to make the subject "the mother of all battles".[2] He represents the Workers' Force in the unrest that arose out of the opposition to the reform law.
