Louis’s later life starts when he was offered a job as a famous chemist's, Antoine-Jerome, assistant. Louis enjoyed the job of one of his dreams, a chemist. In 1847, as Antoine’s assistant, Louis studied crystals and the way they grew. That was where his drawing skills came in.

In 1848, his mother died. He blamed her death on her worries about his safety with creams and medicines. The next year on May 29, 1849, he got married to Marie Laurent. On his wedding day, he was so caught up in his work with his crystals that he had to be reminded to go to his own wedding! He and Marie had five children during their 46 year marriage, the marriage ended when Pasteur died.

Later in 1849, Louis became the professor of chemistry at the University of Strasbourg. University of Strasbourg is in Northeastern France. Although he was a professor, he always found time to continue his studies with crystals. In 1850 Jeanne Pasteur was born. Then, in 1854, he took a new teaching job as Dean of Sciences at University of Lille after they moved to Lille in northern France.  When Jeanne was 9, she died of typhoid fever.