Born in Leuven, Triangle joined the youth section of the Confederation of Christian Trade Unions in 1982.
In 2011, he moved to become general secretary of the European Trade Union Federation for Textiles, Clothing and Leather.
This became part of IndustriALL – European Trade Union in 2012, with Triangle appointed as a deputy general secretary.
[1][2] In April 2023, Triangle was appointed as acting general secretary of the International Trade Union Confederation, following the dismissal of Luca Visentini.
His priorities were enacting governance and financial reforms, defending workers' rights, and campaigning for a new social contract.