Jacob Ludwig Carl Grimm was born on January 4, 1785, in the town of Hanau, Germany, to Dorothea and Philipp Grimm. Jacob was the eldest of several siblings, including the brother born soonest after him, Wilhelm. Their father worked as a lawyer, and both Jacob and Wilhelm eventually pursued legal studies at the University of Marburg.
Jacob went on to work as a royal librarian for Napoleon's brother, Jérôme, king of Westphalia, in 1808, and later worked as a municipal auditor. In 1816, Jacob joined his brother to work at a library in Kassel, where Wilhelm had obtained a position as secretary.