Day was born on December 30, 1984 in Spokane, Washington. She moved to Southern California at age three, and grew up in and around San Diego, California, with her family. She began singing at a young age at the First United Methodist Church in Chula Vista, California. Day also began taking dance lessons at age 5 (a discipline she continued into her 20s). She attended Valencia Park Elementary School which she credits with fostering her interest in performing arts. At age 12, Day was introduced to the sounds of prominent jazz vocalists like Billie Holiday, Ella Fitzgerald, and Dinah Washington, all of whom she counts as early influences on her sound. Day attended the San Diego School of Creative and Performing Arts where she graduated in 2003.
After high school, Day worked about 20 different jobs including one as a children's entertainer. In 2010, Stevie Wonder's then wife, Kai Millard, noticed Day performing at a strip mall and brought her to the attention of her husband. Day received a call from Wonder himself soon after. No immediate partnership was formed, but the two reconnected around a year later. Wonder introduced Day to producer Adrian Gurvitz at that time. Gurvitz would eventually collaborate on Day's debut album a few years later.
Day earned a record deal with Warner Bros. Records in part because of the popularity of her numerous unplugged covers and mashups on her YouTube channel, most of which were filmed in her sister's bedroom in San Diego. Her covers include Jessie J's "Mamma Knows Best", Eminem's "Lose Yourself", and Muse's "Uprising" among others. She was also known for mashups including one that patched together The Notorious B.I.G.'s "Big Poppa" with Marvin Gaye's "Let's Get It On" and another that combined Amy Winehouse's "He Can Only Hold Her" and Lauryn Hill's "Doo Wop (That Thing)".
During that time, Day was also working with Gurvitz on around 40 original songs. Other producers and contributors to what would eventually become her debut studio album included Raphael Saadiq, Questlove, James Poyser, DJ Jazzy Jeff, and The Dap-Kings. Day performed at the 2014 Sundance Film Festival and caught the eye of director, Spike Lee. He volunteered to direct the video for her single, "Forever Mine". Day has also performed at the 2015 BET Awards, the closing ceremonies of the 2015 Special Olympics, the Essence Music Festival, and on television shows like Jimmy Kimmel Live!, Good Morning America, and numerous others. She also performed Nina Simone's "Mississippi Goddam" for the soundtrack for the Netflix documentary, What Happened, Miss Simone?.
Her first studio album, Cheers to the Fall, was released on August 28, 2015. It was met with critical acclaim with NPR's Katie Presley saying Day's voice has "Eartha Kitt's unflappable confidence, Amy Winehouse's effortless grasp of classic jazz, Billie Holiday's access to raw emotion and Adele's range and pop sensibility." The album was nominated for Best R&B Album and "Rise Up" was nominated for Best R&B Performance at the 58th Grammy Awards in 2016 (an event at which she also performed). The album also peaked at number 48 on the Billboard 200 list. In September 2015, "Rise Up" was used in an advertisement for Beats by Dre that featured tennis player, Serena Williams. In November and December 2015, Day appeared alongside Stevie Wonder in an Apple TV commercial in which the two sang Wonder's song, "Someday at Christmas".
Her first national tour took place in August and September 2015 when she opened up for Lenny Kravitz. In October 2015, she sang "Rise Up" at The White House and again performed the song for A&E's live special, Shining a Light: A Concert for Progress on Race in America.
In May 2016, Day entered into an agreement with McDonald's and Coca-Cola that saw her image on around 50 million cups at McDonald's. The partnership is part of the "Share a Cup" lyrics program and will also feature lyrics from Day's "Rise Up". Purchasers of the cups at McDonald's could enter a sweepstakes that would have allowed them to see Day perform at the Essence Music Festival in June 2016. Her Cheers to the Fall Tour is set to begin in November 2016 and will start in her hometown of San Diego.
Day performed on the second day of the 2016 Democratic National Convention in Philadelphia to rousing applause. She followed immediately after a moving address by Mothers of the Movement, a group of black mothers who had lost a child through encounters with police and gun violence.
In December 2016, Andra Day received the Powerhouse Award at the Billboard Women in Music event. When asked what makes a 'powerhouse' powerful to others, Day responded, "I think you just remind them of their value, you remind them of their purpose. You remind them that you are not here just to exist, you're here to impact people in their lives...I think it just reinforces that."