Davis was born on her grandmother's farm, on the former Singleton Plantation, in St. Matthews, South Carolina. She is the second youngest of six children. Her father, Dan Davis, was a horse trainer; her mother, Mary Alice, was a maid, factory worker, and homemaker, as well as a civil rights activist. Her family moved to Central Falls, Rhode Island a few months after she was born. Davis has described herself as having "lived in abject poverty and dysfunction" during her childhood.
Davis partially credits her love of stage acting with her involvement in the arts at her alma mater, Central Falls High School. Davis majored in theatre at Rhode Island College, graduating in 1988; in 2002 she received an honorary doctorate in Fine Arts from the college. She was involved in the federal TRIO Upward Bound and TRIO Student Support Services programs. While Davis was a teenager, her talent was recognized by Bernard Masterson when, as director of Young People's School for the Performing Arts in West Warwick, Rhode Island, he awarded Davis a scholarship into that program.
She also attended the Juilliard School for four years, as a member of the Drama Division's Group 22 (1989–1993).
In 2001, she won the Tony Award and a Drama Desk Award for her portrayal of Tonya in King Hedley II, a "35-year-old mother fighting eloquently for the right to abort a pregnancy." She has also won another Drama Desk Award for her work in a 2004 off-Broadway production of Intimate Apparel by Lynn Nottage.
Davis appeared in numerous films, including three films directed by Steven Soderbergh – Out of Sight, Solaris and Traffic, as well as Syriana, which Soderbergh produced. Viola was also the uncredited voice of the parole board interrogator who questions Danny Ocean (George Clooney) in the first scene in Ocean's Eleven. She also gave brief performances in the films Kate & Leopold and Antwone Fisher. Her television work includes a recurring role in Law & Order: Special Victims Unit; starring roles in two short-lived series, Traveler and Century City; and a special guest appearance in "Badge", a Law & Order: Criminal Intent episode. In 2008, Davis played Mrs. Miller in the film adaptation to the Broadway play Doubt, with Meryl Streep, Philip Seymour Hoffman, and Amy Adams. Davis was nominated for several awards for this performance, including a Golden Globe and an Academy Award for Best Supporting Actress.
On June 30, 2009, Davis was inducted into The Academy of Motion Picture Arts and Sciences. On June 13, 2010, Davis won her second Tony Award for her role as Rose Maxson in a revival of August Wilson's Fences. She is the second African-American woman to win the award, after Phylicia Rashād.
Davis played the role of Dr. Minerva in It's Kind of a Funny Story (2010), a coming-of-age film written and directed by Anna Boden with Ryan Fleck, adapted from the 2006 novel by Ned Vizzini. In August 2011, Davis played the role of Aibileen Clark in the screen adaptation of Kathryn Stockett's novel The Help, directed by Tate Taylor. For her performance, Davis garnered great critical acclaim, and eventually received two Screen Actors Guild Awards, as well as her second Academy Award nomination, which she ultimately lost to her good friend Meryl Streep. She also received Golden Globe Award and BAFTA nominations for the same performance.
In 2012, Time magazine listed Davis as one of the most influential people in the world. Also in 2012, Glamour magazine named Davis Glamour's Film Actress of the year. On June 12, 2012, Davis was presented with the Women in Film's Crystal Award by her friend and Oscar rival that year Meryl Streep. On June 25, 2012, The Walk of Fame Committee of the Hollywood Chamber of Commerce announced that Davis was part of the new group of entertainment professionals who have been selected to receive stars on the Hollywood Walk of Fame in 2013.
In April 2013 it was reported that Davis is in talks to play a starring role in the untitled Michael Mann-directed film that will star Chris Hemsworth and Maggie Casey as his love interest. Legendary Pictures is producing the thriller.
In September 2013, it was announced that Davis would reunite with The Help director Tate Taylor in a biopic of James Brown playing Brown's mother. Her The Help co-star Octavia Spencer was also slated for a role. Davis later revealed that her daughter Genesis would also appear in the movie.
In February of 2014, Davis joined the cast of Shonda Rhimes’ pilot How to Get Away with Murder as the lead character. It was picked up to series for the fall of 2014-15 on May 8, 2014.
Davis married actor Julius Tennon June 2003. They have a daughter, Genesis, whom they adopted as a newborn in October 2011. Davis is stepmother to Tennon's two sons from previous relationships.