Smith was born on September 25, 1968 in Philadelphia, Pennsylvania, to Caroline (Bright), a Philadelphia school board administrator, and Willard Carroll Smith Sr., a refrigeration Engineer. He grew up in West Philadelphia's Wynnefield neighborhood, and was raised Baptist. He has three siblings, sister Pamela, who is four years older, and twins Harry and Ellen, who are three years younger. Smith attended Our Lady of Lourdes, a private Catholic elementary school in Philadelphia. His parents separated when he was 13, but did not actually divorce until around 2000.

In the late 1980s, Smith achieved modest fame as a Rapper under the name The Fresh Prince. In 1990, his popularity increased dramatically when he starred in the popular NBC television series The Fresh Prince of Bel-Air, which ran for six seasons until 1996. After the series ended, Smith transitioned from television to film, and has gone on to star in numerous blockbuster films. He is the only actor to have eight consecutive films gross over $100 million in the domestic box office, eleven consecutive films gross over $150 million internationally, and eight consecutive films in which he starred, open at the number one spot in the domestic box office tally.

Soon after, the two decided to join forces. Smith enlisted a friend to join as the Beatboxer of the group, Clarence Holmes (Ready Rock C), making them a trio. Philadelphia-based Word Up Records released their first single in late 1985 to 1986 when A&R man Paul Oakenfold introduced them to Word Up with their single "Girls Ain't Nothing but Trouble," a tale of funny misadventures that landed Smith and his former DJ and rap partner Mark Forrest (Lord Supreme) in trouble. The song sampled the theme song of "I Dream of Jeannie." Smith became known for light-hearted story-telling raps and capable, though profanity-free, "battle" rhymes. The single became a hit a month before Smith graduated from high school.

Based on this success, the duo were brought to the attention of Jive Records and Russell Simmons. The duo's first album, Rock the House, which was first released on Word Up in 1986 debuted on Jive in March of 1987. The group received the first Grammy Award for Best Rap Performance in 1989 for "Parents Just Don't Understand" (1988), though their most successful single was "Summertime" (1991), which earned the group their second Grammy and peaked at number 4 on the Billboard Hot 100. Smith and Townes are still friends and claim that they never split up, having made songs under Smith's solo performer credit.

Smith spent money freely around 1988 and 1989 and underpaid his income taxes. The Internal Revenue Service eventually assessed a $2.8 million tax debt against Smith, took many of his possessions, and garnished his income. Smith was nearly bankrupt in 1990, when the NBC television network signed him to a contract and built a sitcom, The Fresh Prince of Bel-Air, around him. The show was successful and began his acting career. Smith set for himself the goal of becoming "the biggest movie star in the world", studying box office successes' Common characteristics.

Smith married Sheree Zampino in 1992. They had one son, Trey Smith, born on November 11, 1992, and divorced in 1995. Trey appeared in his father's music video for the 1998 single "Just the Two of Us". He also acted in two episodes of the sitcom All of Us, and has appeared on The Oprah Winfrey Show and on the David Blaine: Real or Magic TV special.

Smith's first major roles were in the drama Six Degrees of Separation (1993) and the action film Bad Boys (1995) in which he starred opposite Martin Lawrence. The latter film was commercially successful, grossing $141,407,024 worldwide — $65,807,024 in North America and $75,600,000 overseas. However, critical reception was generally mixed. In 1996, Smith starred as part of an ensemble cast in Roland Emmerich's Independence Day. The film was a massive blockbuster, becoming the second highest-grossing film in history at the time and establishing Smith as a prime box office draw.

Smith married Actress Jada Koren Pinkett in 1997. Together they have two children: Jaden Christopher Syre Smith (born 1998), his co-star in The Pursuit of Happyness and After Earth, and Willow Camille Reign Smith (born 2000), who appeared as his daughter in I Am Legend. Smith and his brother Harry own Treyball Development Inc., a Beverly Hills-based company named after Trey. Smith and his family reside in Los Angeles, California.

In 1998, Smith starred with Gene Hackman in Enemy of the State. The following year he turned down the role of Neo in The Matrix in favor of Wild Wild West (1999). Despite the disappointment of Wild Wild West, Smith has said that he harbors no regrets about his decision, asserting that Keanu Reeves's performance as Neo was superior to what Smith himself would have achieved, although in interviews subsequent to the release of Wild Wild West he stated that he "made a mistake on Wild Wild West. That could have been better."

Smith's second album was again supported by the release of a film theme song as the lead single: "Wild Wild West", featuring Dru Hill and Kool Moe Dee, topped the Billboard Hot 100 and was certified gold by the RIAA. The album in question, Willennium, reached number five on the Billboard 200 and was certified double platinum by the RIAA. "Will 2K", the second single from the album, reached number 25 on the Billboard Hot 100. Before the end of 1999, a video album was released featuring Smith's seven music videos released to date, which reached number 25 on the UK Music Video Chart. The same year, the Rapper was also featured on The Fresh Prince of Bel-Air co-star Tatyana Ali's single "Boy You Knock Me Out", which reached number three on the UK Singles Chart and topped the UK R&B Singles Chart.

Smith portrayed heavyweight boxer Muhammad Ali in the 2001 biopic Ali. For his performance he was nominated for the Academy Award for Best Actor, and the Golden Globe Award for Best Actor – Motion Picture Drama. In 2002, following a four-year musical hiatus, Smith returned with his third album Born to Reign, which reached number 13 on the Billboard 200 and was certified gold by the RIAA. The album's lead single was Men in Black II theme song "Black Suits Comin' (Nod Ya Head)", which reached number three on the UK Singles Chart. Later in the year, Smith's first compilation album Greatest Hits was released, featuring songs from his three solo albums as well as those produced with DJ Jazzy Jeff.

2003 saw Smith return for Bad Boys II, the sequel to the 1995 film Bad Boys and the second installment in the Bad Boys series, the film follows detectives Burnett and Lowrey investigating the flow of ecstasy into Miami. Despite receiving generally negative reviews, the film was a box office success, grossing $270 million worldwide.

Smith's latest album Lost and Found was released in 2005, peaking at number six on the Billboard 200. Lead single "Switch" reached the top ten of both the Billboard Hot 100 and the UK Singles Chart. In 2005, Smith was entered into the Guinness Book of World Records for attending three premieres in a 24-hour time span.

Smith and his son Jaden played Father and son in the 2006 biographical drama The Pursuit of Happyness In the film Smith portrays Chris Gardner. Smith first became interested in making a film about Gardner after seeing him on 20/20 and connected with him during production. The film, along with Smith's performance, received praise.

Smith gave $1.3 million to charities in 2007, of which $450,000 went to two Christian ministries, and $122,500 went to three Scientology organizations; the remaining beneficiaries included "a Los Angeles mosque, other Christian-based schools and churches, and ... the Yitzhak Rabin Memorial Center in Israel." Smith and his wife have also founded a private elementary school in Calabasas, California, the New Village Leadership Academy. Federal tax filing showed that Smith donated $1.2 million to the school in 2010.

In 2008 Smith was reported to be developing a film entitled The Last Pharaoh, in which he would be starring as Taharqa. It was in 2008 that Smith starred in the superhero movie Hancock. Hancock has grossed $227,946,274 in the United States and Canada and $396,440,472 in other territories for a worldwide total of $624,386,746.

Smith donated $4,600 to the 2008 presidential campaign of Democrat Barack Obama. On December 11, 2009, Smith and his wife hosted the Nobel Peace Prize Concert in Oslo, Norway to celebrate Obama's winning of the prize.

On August 19, 2011, it was announced that Smith had returned to the studio with Producer La Mar Edwards to work on his fifth studio album.

In 2012, Smith stated he supported legalizing same-sex marriage.

In 2013 Smith starred in After Earth with his son Jaden. The film was a disappointment at the domestic box office and was panned critically. Calling the film "the most painful failure in my career." Smith ended up taking a year and a half break as a result.

Smith has been ranked as the most bankable star worldwide by Forbes. As of 2014, 17 of the 21 films in which he has had leading roles have accumulated worldwide gross earnings of over $100 million each, five taking in over $500 million each in global box office receipts. As of 2016, his films have grossed $7.5 billion at the global box office. For his performances as boxer Muhammad Ali in Ali (2001) and stockbroker Chris Gardner in The Pursuit of Happyness (2006), Smith received nominations for the Academy Award for Best Actor.

Smith starred opposite Margot Robbie in the romance drama Focus. He played Nicky Spurgeon, a veteran con Artist who takes a young, attractive woman under his wing. Focus was released on February 27, 2015. Smith was set to star in the sci-fi thriller Brilliance, an adaptation of Marcus Sakey's novel of the same name scripted by Jurassic Park Writer David Koepp, but he left the project to work on the Ridley Scott-produced Sports drama Concussion.

In 2016, Smith played Deadshot in the supervillain team-up action film Suicide Squad. Smith's participation in the film meant choosing it over a role in Independence Day: Resurgence, which he said would be like "clinging and clawing backwards." Later that year, Smith starred in Director David Frankel's drama Collateral Beauty, playing a New York advertising executive who succumbs to a deep depression after a personal tragedy. Weeks after signing Smith onto the film, his Father was diagnosed with cancer, from which he died in 2016. As part of his role required him to read about religion and the afterlife, he was brought closer to the elder Smith, calling the experience "a beautiful way to prepare for a movie and an even more majestic way to say goodbye to my Father."

His most recent film, Bright was distributed via Netflix on December 22, 2017. An urban fantasy, it was the most expensive film for Netflix to date. Smith collaborated with his Director from Suicide Squad, David Ayer.

Smith will voice Lance Sterling, a spy, in Spies in Disguise, which sees Lance having to team up with the nerdy Inventor who creates Lance's gadgets, voiced by Tom Holland. The film is scheduled to be released on January 18, 2019. Next, Smith will portray The Genie (originally played by Robin Williams in the 1992 animated film) in a live-action film adaptation of Disney's Aladdin directed by Guy Ritchie which is scheduled to be released on May 24, 2019. Lastly, Smith will appear as an Assassin who faces off against himself, a clone who is younger and in his prime in Ang Lee's Gemini Man, scheduled for release on October 4, 2019.