He is primarily known for the numerous operetta librettos that he wrote for composers such as Leo Fall, Jean Gilbert, Emmerich Kálmán, and Ralph Benatzky.

In 1901 he published a book on the painters of Augsburg during the Baroque and Roccoco eras, but then turned his activity to the theatre.

[1][2] Welisch's parallel career as a librettist began in 1905 when he and Rudolf Bernauer co-wrote the libretto for Leo Fall's first operetta Der Rebell.

During his career he wrote or co-wrote over 20 librettos for operettas and musical theatre works as well as two stage comedies.

His final work was the libretto for the operetta Venedig in Wien composed by Rudi Gfaller.