Goodwin was born Jennifer Michelle Goodwin in Memphis, Tennessee, on May 22, 1978, to Tim Goodwin, who formerly owned and operated a recording studio, and his wife, Linda, a former educator. She changed her name from "Jennifer" to "Ginnifer" to distinguish her name, and to assist in pronunciation of her name, in her regional dialect. Her younger sister, Melissa Goodwin, is a stop-motion animator on shows such as the Emmy award-winning Robot Chicken, on which Ginnifer herself has also appeared as voice talent.
Goodwin was affiliated with the North American Federation of Temple Youth and was active in BBYO at the Jewish Community Center in Memphis growing up; she had a bat mitzvah. After graduating from Lausanne Collegiate School in 1996, Goodwin attended Hanover College (majoring in Theatre) for one year before moving on to Boston University's College of Fine Arts, where she received a "Bachelor of Fine Arts in Acting" with honors in 2001.
Goodwin first had roles in the popular NBC television programs Law & Order and Ed before appearing in the Comedy Central television movie Porn 'n Chicken. She later had substantial roles in the films Mona Lisa Smile, Win a Date with Tad Hamilton!, Walk the Line — in which she portrayed Vivian Liberto, Johnny Cash's first wife — and Birds of America. She also played Dori Dumchovic in the dark comedy Love Comes to the Executioner. Goodwin played a leading role as Margene Heffman, the third wife in a polygamous family, on the HBO original series Big Love, which concluded on March 20, 2011.
She also starred as Gigi in He's Just Not That into You, which was released in February 2009. For this role, she received a nomination for the "People's Choice Award for Breakout Movie Actress". In April 2009, she began filming Ramona and Beezus. In 2008, MaxMara honored Goodwin with a "Face of the Future" award, an award recognizing up and coming women in film.
In 2011, Goodwin was cast to play the starring role of Mary Margaret Blanchard, a teacher in Storybrooke, Maine, who is actually Snow White, in the revisionist fantasy adventure television program Once Upon a Time, which debuted on ABC.
In 2013, Goodwin confirmed on her Twitter account that she would be portraying the role of Gwen on Disney's animated series Sofia the First. Later that year, she starred in the TV movie Killing Kennedy, an adaptation of the 2012 novel of the same name.
Goodwin was a vegan and a spokesperson for Farm Sanctuary's "Adopt-A-Turkey Project" in 2009, having adopted a whole flock herself. She revealed on Jimmy Kimmel's show that she gave up being a vegan after experiencing undisclosed health issues. Not long after meeting him on set, Goodwin engaged romantic relationship with fellow Once Upon a Time co-star and on-screen husband Josh Dallas. In 2013, the couple announced their engagement and that they were currently expecting their first child. They married on April 12, 2014 and their son, Oliver Finlay Dallas, was born on May 29, 2014. On November 17, 2015 it was announced that Goodwin and Dallas were expecting a second child.