Elfman was born Jennifer Mary Butala in Los Angeles, California, the youngest of three children, to Sue (Grace) Butala, a homemaker, and Richard Butala, a Hughes Aircraft executive. Her father's younger brother, Elfman's uncle, is Tony Butala, lead singer since 1958 of the American vocal trio The Lettermen. She is of Croatian ancestry on her father's side and was raised Roman Catholic.
Elfman attended high school at the Los Angeles County High School for the Arts and then attended college at California State University, Northridge (CSUN).
Elfman began her professional career as a dancer, appearing in the music videos for Depeche Mode ("Halo" in 1990), Anthrax (1993's song "Black Lodge"), Chris Isaak (1995's "Somebody's Crying") and toured with the rock band ZZ Top on their 1994 tour as a "Legs Girl". After appearing in television commercials, Elfman was cast in the short-lived 1996 American sitcom entitled Townies on ABC . In 1997 Elfman was cast in Dharma & Greg on ABC, as Dharma Freedom Finkelstein Montgomery. The show ran for five seasons until its cancellation in 2002.
In 2012, Elfman and her husband Bodhi started their podcast, Kicking and Screaming by Jenna and Bodhi Elfman.
In 2013, Elfman appeared in two NBC comedy series (1600 Penn, and Growing Up Fisher) which were cancelled after a single season.
In 2016, Elfman was cast in the ABC comedy series Imaginary Mary. Like 1600 Penn and Growing Up Fisher, the series was cancelled after its first season.
Elfman met her husband, actor Bodhi Elfman, at a Sprite commercial audition in February 1991. They married on February 18, 1995.
On July 23, 2007, Elfman and her husband's first child, a son, Story Elias, was born in Los Angeles. On March 2, 2010, their son, Easton Quinn Monroe, was born.
Elfman is a member of the Church of Scientology.
In 2005, Elfman appeared at the Scientology-backed Citizens Commission on Human Rights' "Psychiatry: An Industry of Death" museum grand opening and she and husband Bodhi are listed on the organization's website as members of the board of advisers from the arts, entertainment and media community.
On May 24, 2006, she was the keynote speaker at the Human Rights Hero Award event in participation with the Scientology-affiliated groups Youth for Human Rights International and Artists for Human Rights (AFHR), an organization formed with the purpose of bringing artists together with the common cause of raising awareness of human rights around the world.
On March 27, 2008, Elfman and Charlie Sheen co-hosted the Scientology-affiliated New York Rescue Workers Detoxification Project Charity Event at Geisha House in Hollywood.
Elfman has participated in a number of fundraising activities, including: donating an hour of her time for auction; donating a print of her lips; participating in a telethon fundraiser; hosting a comedy show; and, asking for charity donations instead of birthday presents.
Elfman has also participated in awareness-raising initiatives including: modelling for a fashion show; reading to schoolchildren as part of the National Education Association Read Across America program; and, hosting a party at her house to raise awareness for a number of causes headed by the Environmental Working Group.
Elfman is on the Board of Directors of the Dizzy Feet Foundation.