The 47-year-old Belgian worked for Tour de France organiser ASO in a communications role in the 1990s and later moved into the race organisation side of the company. In 2005 he joined the Phonak team in a managerial role but the team ended at the end of 2006 after Floyd Landis was stripped of his Tour de France title.
When Phonak team owner Andy Rihs set up the BMC Racing team in 2007, Lelangue followed across as a directeur sportif and stayed for six-and-a-half years. He left the day after the 2013 Tour de France, which had been a disappointing one for the team.
Having previously helped establish the Tour of Qatar while at ASO, Lelangue moved to the country to work on the organisation of the 2016 UCI Road World Championships and has since worked for the governing body as a technical advisor.
"I'm really happy and proud to join Lotto Soudal and be part of such a nice project for the future," Lelangue said.
Lelangue will be joined at the team by performance manager Kevin De Weert, who worked at the Belgian Federation for the past three years, and at LottoNL-Jumbo before that.
The change at the top of the Lotto Soudal team comes just nine months after De Geyter joined the team ahead of the 2018 season, in a restructuring that saw previous boss Marc Sergeant move into a purely sporting role.
A former rider agent, De Geyter ruffled feathers during his time at the team, most notably over the departure of long-time talisman Andre Greipel, who branded De Geyter a liar during fractious contract negotiations that ultimately saw the German forced to make way for young Australian sprinter Caleb Ewan.
In the aftermath, one rider called Sergeant and told him: "Marc you have to watch out because the family is falling apart. Paul is looking at this as a business, but it isn't a business."
On Monday it was announced that De Geyter's contract had been terminated by mutual consent, with the team stating that "the two parties came to the conclusion that the perspective on the future strategy of the team differed too much from each other to continue the partnership."