Born October 15, 1959, in the city of Fall River, Massachusetts, he was raised by his French-Canadian father, Emeril Jr., and his Portuguese mother, Hilda.

While working at a local Portuguese bakery, the teenaged Lagasse developed a penchant for cooking. In 1973, he enrolled in the culinary arts program at Diman Regional Vocational Technical High School. Also a talented percussionist, Lagasse led the high school drum squad, playing at dances, banquets, and numerous local religious festivals.

Upon his high school graduation, Lagasse was offered a scholarship to the New England Conservatory of Music, but decided to pursue a career as a professional chef instead. He spent the next year studying at Johnson & Wales University in Providence, Rhode Island. To pay his tuition, Lagasse took a job at a local restaurant, where he met fellow student Elizabeth Kief. The two married in October 1978, a few months after Lagasse completed his course work.

Lagasse polished his skills in Paris and Lyon, France, before returning to the United States, where he spent the next few years working in fine restaurants throughout the Northeast and at Telemark Lodge in Cable, Wisconsin for Tony Wise. He graduated from Johnson & Wales University in 1978; the university later awarded him an honorary doctorate.

In 1982, Lagasse replaced Paul Prudhomme as executive chef of the famed New Orleans restaurant Commander's Palace. This demanding position, which required Lagasse to work 18 hours a day, put a strain on his marriage.

After the birth of daughters Jessica and Jillian, Elizabeth Kief and Lagasse divorced. Lagasse married a second time to fashion designer, Tari Hohn, but that too, ended in divorce. Lagasse married a third time on May 13, 2000 to real estate broker, Alden Lovelace. He and Lovelace had a son, Emeril John Lagasse IV, on March 2003, and a daughter, Meril Lovelace Lagasse, on December 10, 2004.