Following the marriage of her older sister Mary to Harvard Professor Cornelius Conway Felton (later president of Harvard University), she began socializing with a group of intellectuals in Cambridge, Massachusetts. In 1846, she met scientist Louis Agassiz at a dinner with Mary and her husband. Though they wanted to marry, he still had a wife and three children (Pauline, Ida and Alexander) in Switzerland. His wife died in 1848. In December 1849—when socially acceptable to wed—Lizzie's father gave his blessing. They married on April 25, 1850 in Boston, Massachusetts at King's Chapel. Agassiz organized the household and took care of the finances and the children. She developed strong relationships with her step-children, Alexander, Ida, and Pauline, and her grandchildren. She had no children of her own.