Jennifer Lynn Siebel was born on June 19, 1974 to Judy and Ken Siebel in San Francisco, California. The oldest of four daughters, Jennifer was raised in Ross, California, spent her summers on a ranch in Montana, and attended the Branson School.

Jennifer pursued higher education at Stanford University, earning a Bachelor's degree in 1996 and later a Master's of Business Administration in 2001 with honors. She studied with a focus on Third World Development and Conservation Policy. Jennifer took her studies further by working in Africa, Latin America, and Europe on assignments with Conservation International, a global environmental organization, where her primary focus was providing micro-enterprise opportunities to women and working with indigenous communities. She speaks conversational Spanish. Upon graduation, Jennifer was determined to follow her long held passion to work in the arts and pursued acting. She moved to Los Angeles and landed roles in film, television, and theater including Something’s Gotta Give, Rent, In the Valley of Elah, Mad Men, Life, Numb3rs, Trauma and Strong Medicine.

While in Hollywood, she also founded Girls' Club Entertainment LLC, an umbrella entertainment company to develop and produce independent films with strong social, political, and cultural significance. Jennifer set out to develop female-centric, transnational stories, in addition to young female sports and arts stories with messages of hope and inspiration.

In the summer of 2008, Jennifer married Gavin Newsom, Mayor of San Francisco. She returned to the Bay Area and began devoting her time to fulfilling her many duties as the First Lady of San Francisco. Jennifer's primary focus has been supporting organizations and causes that help empower women and girls.

Her latest endeavor is writing, directing, and producing the documentary, Miss Representation, which explores how mainstream media directly contributes to the under-representation of women in positions of power and influence by cultivating and promoting limiting and often disparaging portrayals of women. Accompanied by a social outreach campaign, Jennifer hopes to celebrate women's progress throughout American history and motivate calls to action towards achieving greater equality.

In May 2010, Jennifer partnered with the Professional Business Women of California to create The First Lady’s Young Women’s Summit to help empower high school girls in the Bay Area. The Young Women’s Summit is a daylong program designed to educate young women about media literacy, introduce them to successful women mentors, and instill confidence in them to pursue their true passions. Many of the activities underscored the themes found in Jennifer’s documentary, Miss Representation.

Jennifer and Gavin welcomed their daughter, Montana Tessa Siebel Newsom in September 2009. They are expecting the arrival of their second child, a baby boy, in 2011.