In 1842, Beyaert went to Brussels where he kept a small bookshop to earn his living and where he enrolled at the Royal Academy of Fine Arts to attend architectural courses.

This cooperation with the architect Wynand Janssens resulted in a lavish neo-Baroque building heavily influenced by the new style propagated in Paris, known as Second Empire.

The critical success that it enjoyed, together with Beyaert's connections with the powerful Liberal Party, led to many other commissions, beginning with the De Brouckère fountain (1866), now on the Square Jan Palfijn/Jan Palfijnplein in Laeken.

Other works included the Antwerp office of the National Bank of Belgium (1874–1879), built on a clever triangular plan, Tournai railway station (1875–1879, damaged in World War II), and the Kegeljan-Godin House (1878–1880) in Namur.

With his passion for study and novelties (Beyaert possessed an extensive library on the history of architecture and the decorative arts), his buildings became increasingly charged with historical ornamentation, without however lacking a clear structural basis.

In an architectural contest following the covering of the river Senne (1867–1871), Beyaert's Maison des Chats or Hier is't in den kater en de kat (loosely, "House of Cats") took first prize.

In this respect, Beyaert would become instrumental in the formation of a new generation of architects, such as Paul Hankar and Victor Horta, that would play an important part in the evolution of Art Nouveau architecture.