Jennifer Love Hewitt was born on February 21, 1979, in Waco, Texas. She grew up in Nolanville, Central Texas, and has close kinship ties in parts of Arkansas. Her parents, Patricia Mae, a speech-language pathologist, and Herbert Daniel Hewitt, a medical technician, divorced when she was young.

Jennifer and her older brother Todd were raised by their mother. From a young age, Jennifer was attracted to music and performed at various events. At age three, she sang "The Greatest Love of All" at a livestock show. By age five, she was taking tap dancing and ballet lessons. She became a member of the Texas Show Team, which toured the Soviet Union and Europe.

Jennifer began her career as a child actress and singer, appearing in national television commercials before joining the cast of the Disney Channel series Kids Incorporated from 1989 to 1991.

She gained fame for her role as Sarah Reeves Merrin on the Fox teen drama Party of Five from 1995 to 1999. She rose to stardom as Julie James in the horror films I Know What You Did Last Summer in 1997 and its 1998 sequel.

She also starred in the teen comedy film Can't Hardly Wait in 1998.

Her other notable films include Heartbreakers in 2001, The Tuxedo in 2002, and the two Garfield live-action films from 2004 to 2006. She starred as Melinda Gordon on the CBS supernatural drama Ghost Whisperer from 2005 to 2010, Riley Parks on the Lifetime drama series The Client List from 2012 to 2013, and Special Agent Kate Callahan on the CBS crime drama Criminal Minds from 2014 to 2015.

Since 2018, she has played Maddie Buckley on the Fox first-responder procedural 9-1-1.

In music, Jennifer has released four studio albums. Her debut album, Love Songs, was released in 1992 exclusively in Japan when she was 12. She went on to record Let's Go Bang in 1995, Jennifer Love Hewitt in 1996, and BareNaked in 2002. BareNaked became her first album to chart in the United States, peaking at number 37 on the Billboard 200 chart.

Her most successful single on the Billboard Hot 100 chart was the 1999 release "How Do I Deal," which peaked at number 59. In addition to music and acting, she has served as a producer on some of her film and television projects. She has appeared in several magazines' lists of the world's most beautiful women.

Jennifer has received numerous awards and nominations throughout her career. She won the Saturn Award for Best Actress on Television for Ghost Whisperer in 2007 and 2008.

She was nominated for the Golden Globe Award for Best Actress in a Miniseries or Television Film for The Client List pilot film in 2010. She has also won the Blockbuster Entertainment Award for Favorite Actress in a Horror film for I Still Know What You Did Last Summer in 1999 and the People's Choice Award for Favorite Female Performer in a New Television Series for Time of Your Life in 2000.

Jennifer married actor Brian Hallisay in 2013, and they have three children: Autumn, Atticus, and Aidan. The couple met on the set of Love Bites and reconnected on the set of The Client List in 2012.

Jennifer has credited her mother, who passed away from cancer in 2012, for inspiring her to create her own family.