He taught at the Pennsylvania Academy of the Fine Arts for more than twenty years and is best remembered as an animalier.

[4] In Philadelphia's Rittenhouse Square is his famous bronze Billy (1914) – a sculpture of a goat that is known to be a favorite of children who love to sit on it – which was given to the City of Philadelphia by Eli Kirk Price II through the Fairmount Park Art Association (now the Association for Public Art).

Laessle's studio was close to the Philadelphia Zoo, which allowed him easy access to animal models.

[6][4] Laessle collaborated with Grafly on the General Galusha Pennypacker Memorial for Philadelphia's Logan Circle.

Grafly's concept was to depict Pennypacker as a bare-chested Roman general astride a chariot-like cannon, and flanked by tigers.

[2] In 1951, Laessle won the J. Sanford Saltus Award for Outstanding Achievement in the Art of the Medal from the American Numismatic Society.