Philippe has become the seventh King of the Belgians, following the abdication of his father King Albert II after 20 years on the throne.
He was sworn in during a ceremony in parliament, saying: “I swear to respect to constitution and the laws of the Belgian people, to maintain the independence of the country and to safeguard the territory.”
Philippe, 53, paid homage to his father as he stepped into his shoes.
“Sire, for 20 years you have maintained confidence by showing that on one hand you’re close to everybody, warm and deeply human – and on the other hand, you’re full of attention and commitment while doing your tasks as head of state,” the new king told parliament.
Celebrations for Philippe’s swearing-in have been combined with festivities already planned for Sunday, Belgium’s National Day.
Tensions between the Dutch-speaking and French communities creates frequent political instability. Like his father before him, King Philippe will be expected to bridge that divide.