Catharina Ingelman-Sundberg has been writing for many years. She started her career as a marine archeologist and spent fifteen years investigating the bottom of oceans all over the world. In 1999 Catharina was awarded the Lars Widding "Author of the Year" award for her historical novels. After several years of writing historical novels, and whilst working as a full-time journalist, she got her international breakthrough. Her first book in the humorous series about The League of Pensioners. In 2012, The Little Old Lady Who Broke All the Rules was published and hit the bestseller charts in several countries including the United Kingdom, South Korea,France, Italy and Sweden. The books about The League of Pensioners have been translated into 29 languages and sold in over 40 countries.

In 2015 Catharina was awarded the Italian literature prize Premio Roma for The Little Old Lady Who Broke All the Rules (La banda degli insoliti ottantenni). In 2018, the humorous novel  Krutgummor på Krigsstigen was published in Sweden and hit the bestseller chart. In 2020, Goda rån är dyra, the fourth title in The League of Pensioners series, was published. The book is sold in Sweden and was published in Poland, South Korea, and the United Kingdom (by Pan Macmillan) in October 2023. The fifth and last book in the series entitled Det rånar sig nog was published in September 2022 and was nominated to FeelGood book of 2023.

Landet som försvann (The Land that Vanished) was published in September 2024. It is the first of a series of historical novels based on the latest research findings about Doggerland, a Stone Age culture found in the sea at the Dogger's Banks in the North Sea.