Kevin Scott Richardson was born on October 3, 1971 in Lexington, Kentucky, the son of Ann C. (née Littrell), homemaker, and Jerald Wayne Richardson, Sr, an outdoorsman and handyman. He is the youngest of three boys, and is a first cousin of fellow Backstreet Boys member Brian Littrell.

After graduating high school in 1990, Richardson was torn between entering the Air Force to join the Air Force band, or following the lure of performing by attending the New York American Music and Dramatic Academy in Manhattan. With encouragement from his father, Richardson flew to Orlando, Florida with his best friend Jimmy, where he earned a living as a model, writing music, performing in dinner clubs, taught ballroom dancing as a certified Latin and ballroom dance instructor and was an extra for the film My Girl. In Florida, he got a job as a cast member and performer at Walt Disney World. He played various characters including Aladdin, one of the Teenage Mutant Ninja Turtles, Prince Eric, Tigger, and Sebastian the Crab in the Little Mermaid show. He was also a backstage tour guide. At nights, he did dinner theater, playing an Italian gangster in a musical review performing various songs from the musical "Chicago," "Guys and Dolls" and "Cabaret."

In June 1991, Richardson got the call from his mother, telling him that his father had taken a turn for the worse with his colon cancer. (Richardson's father was originally diagnosed in October 1990.) Richardson dropped everything and moved back home to Kentucky where he got a job and stayed with his family. On August 26, 1991, just two months later, Richardson's father lost his battle with cancer. This was a devastating blow to Richardson, as he had lost not only his father, but a friend and mentor. He stayed in Kentucky for almost a year, then after encouragement from his mother, he went back to Florida to follow his dreams of a music career. He got a job with a friend who had written a musical, he gave him a part and helped him get back on his feet again. Richardson was once engaged to his high school sweetheart, Beth, when he was 19, but they decided they were too young to get married and weren't ready, plus Beth fell in love with someone else and broke his heart.

In 1993, Richardson joined a new group called Backstreet Boys. After he joined, the group was still looking for one more member so Richardson called Brian Littrell, who is Richardson's maternal first cousin (Littrell's father and Richardson's mother are brother and sister), to ask him to audition for the group. Littrell was immediately accepted, and the next day he joined the group. After Littrell joined, the quintet took shape.

Richardson has been married to Kristin Kay Willits, a Dancer, Actress, Photographer and model, since 2000. They met when they both worked at Disney World. Kristin was playing the character of Belle from Beauty and the Beast. Kristin was also featured in one of the Backstreet Boys earliest videos "I'll Never Break Your Heart" and one of the Dancers at the American Music Awards in 1999. Their engagement, along with bandmate and cousin Brian Littrell's to Leighanne Wallace, was announced on MTV in February 2000, and the couple married on June 17, 2000, at The Cathedral Domain Camp and Conference Center in rural Lee County in eastern Kentucky. Together they have two sons: Mason Frey was born on July 3, 2007 and Maxwell Haze was born on July 10, 2013.

Just Within Reach (JWR) was formed by Richardson and started in honor of his father Jerald Wayne Richardson. Richardson wanted to name the foundation after his father, whom he lost to cancer. Richardson formed the JWR foundation to provide environmental education and promote personal responsibility and accountability with regard to the health of the Earth. The foundation was founded in January 2001. He has also run with the Olympic torch for the foundation in Los Angeles, California, on January 15, 2001 and did various events for the foundation. It has been many years since he has done anything with the foundation and reportedly closed it.

During the Backstreet Boys' hiatus in 2003, Richardson went into acting. He played the role of smooth-talking Lawyer Billy Flynn in the Broadway production of Chicago. He was a part of the show in New York City (January 20 – March 9), Pittsburgh (July 26–27), San Francisco (August 6–24) and the West End of London (September 22 – November 1). His performance received rave reviews and surprised even the hardest of critics. and in 2003, he made an appearance on Punk'd where he got punk'd by Ashton Kutcher.

After leaving the group, he returned to performing in Chicago. On November 14, 2006, he returned to New York City with many Chicago alumni for the 10th anniversary of the show. From late November to December 3, 2006, Richardson played the role of Billy Flynn in Toronto, and in Japan in February 2007. A couple years later he returned to Japan with the show in September 2009 through early October, and then in Louisville, Kentucky from October 29 to November 1, 2009.

On November 23, 2008, for the first time since leaving the group, Richardson rejoined his former bandmates on stage in Hollywood Palladium, Los Angeles, performing the encore, "Shape of My Heart" with the group.

Richardson also filmed some movies during his time away from the group. His first film was the TV film in the 2009 Christian drama Love Takes Wing, based on a book by Janette Oke, playing the part of Cyrus in 2009.

Richardson filmed some small independent movies in 2010. He starred in The Bloody Indulgent, a vampire themed musical film, also starred opposite Susan Traylor, Daniela Sea, Pleasant Gehman, Garrett Swann and Michael Maize in Steve Balderson's feature film drama The Casserole Club. Richardson had won an Independent Vision Award for Best Actor in the film at Vision Fest in New York City in 2011. and a short film Unwound in 2011. It is an entry for Producers Guild of America premiere Weekend Shorts Event contest to benefit the Debra Hill Foundation. The short film only took 51 hours from script to final cut.

On December 18, 2011, Richardson headlined a Christmas concert titled "Home for the Holidays" with Rob Gonzalez. The concert was hosted by Montage Beverly Hills luxury hotel and it benefited the Angeles Clinic Foundation of Los Angeles.

In an interview with On Air with Ryan Seacrest on July 24, 2012, Richardson explained that he came back to the group because he realized how much joy singing and music gives him. He cited his holiday show with Rob Gonzalez called "Home for the Holidays" (December 18, 2011 in Los Angeles) which helped him rediscover his love of music and how much he missed it.

In 2013, Richardson and the other Backstreet Boys appeared as fictional versions of themselves in the comedy film This Is the End.

In 2015, Richardson filmed an independent film called If I Could Tell You, a short movie about infertility, which was released in 2016, where he also talked about his struggle in having children.

In July 2016, the Backstreet Boys performed on ABC's Greatest Hits. They have a residency in Vegas that ends February 2018 and starts up again July through November 2018.