He took courses at the Académie Royale des Beaux-Arts from 1900 to 1906 and there became friends with Rik Wouters and Edgard Tytgat.
His style gradually evolved from impressionism and Belgian luminism to a synthetic form of capturing reality.
Verhaegen specialized in painting Walloon folklore: Carnival of Binche (he was soon recognised as the painter of "the Gilles of Binche"), Doudou of Mons, Giants of Ath, Chinelles of Fosses, Chaudia of Leernes, Pasqueye, and so on.
In his book about this artist, Robert Magremanne has named him "the great master of the Walloon folklore".
Verhaegen's works are in many museums of Belgium (Antwerp, Brussels, Charleroi, Ixelles, Liège, Mons) and abroad (Genève, Grenoble, Indianapolis).