After finishing school she worked as a librarian for the Rahway Library Association. Her first book, At the Sign of the Sphinx (1896), was a collection of charades. Her next publications were The Jingle Book and The Story of Betty (1899), followed by a book of verse entitled Idle Idyls (1900). After 1900, Wells wrote numerous novels and collections of poetry.

Carolyn Wells wrote a total of more than 170 books. During the first ten years of her career, she concentrated on poetry, humor, and children's books. According to her autobiography, The Rest of My Life (1937), around 1910 she heard one of Anna Katherine Green's mystery novels being read aloud and was immediately captivated by the unravelling of the puzzle. From that point onward, she devoted herself to the mystery genre. Among the most famous of her mystery novels were the Fleming Stone Detective Stories which—according to Allen J. Hubin's Crime Fiction IV: A Comprehensive Bibliography, 1749–2000 (2003)—number 61 titles.

Today, however, she is best known for her light verse, particularly for several classic limericks, including this one:

A canner exceedingly cannyOne morning remarked to his granny:

  “A canner can can
  Any thing that he can

But a canner can’t can a can, can he?”