Guillaume is a prominent figure in the European campaign technology scene, serving as the CEO of LMP, a company that provides software solutions for political and business clients. Over 1,000 clients have used LMP's software, including the En Marche! movement, which helped Emmanuel Macron win the French presidential election. Prior to LMP, Guillaume was the National Field Director for François Hollande's 2012 presidential campaign, during which he likely developed a keen understanding of the inner workings of political campaigns. He also has a business background, having worked for McKinsey in cities such as Paris and Boston.