Alexander James McLean was born on January 9, 1978, in West Palm Beach, Florida, to Denise (née Fernandez, now Solis) and Bob McLean. He is of Puerto Rican and German ancestry on his mother's side and Scots-Irish and English on his father's side. He is an only child because his twin sisters died during childbirth. He was raised by his mother and grandparents (Ursula and Adolph) as his parents divorced when he was four years old.

In January 1986 at 8 years old, McLean acted in his first role as Little Mike in the 1986 film Truth or Dare?.

In 1990, McLean, his mother and grandparents moved to Kissimmee, Florida, to pursue his acting and singing career. He attended a private acting school, the Florida Academy of Dramatic Arts, for four years, acted in the drama club and in small plays, and modeled periodically.

In 1991 McLean landed a role on the Nickelodeon comedy series Hi Honey, I'm Home! as a kid named Skunk. However, he was cut from the show due to being too tall. His only known appearance on the show is in the pilot episode, which Nickelodeon aired in 1999 as part of its birthday celebration.

In 1992, McLean was a contestant in the real-life live-action game show, Nickelodeon Guts. In April 2002, McLean made a guest appearance the episode titled "Duped" in season 2 of Static Shock, a cartoon which ran from 2000–2004.

McLean, Nick Carter, Howie Dorough, Kevin Richardson, and Brian Littrell formed the pop group Backstreet Boys in 1993. The group became very successful in the late 90s-early 2000s. In 2013 they celebrated their 20th anniversary and released a new album called In a World Like This.

In March 2008, McLean performed his first two solo shows (as himself) at the Anaheim House of Blues and The Roxy in Los Angeles. The show consisted of his solo material and a solo version of the Backstreet Boys hit, "Incomplete". The solo tour continued through Europe in May and June, in parallel to Backstreet Boys tour. While creating his solo project, McLean worked with the OneRepublic vocalist Ryan Tedder, producers Dan Muckala and Kristian Lundin, plus the former NSYNC member, JC Chasez. On January 20, 2010, Have It All, was released in Japan. He confirmed on the Backstreet Boys cruise in December 2010 that the US version would be released on February 8, 2011.

McLean married Rochelle Deanna Karidis, a makeup/hair Stylist, whom he credits for helping him overcome his addiction, on December 17, 2011, in Beverly Hills, California. The rest of the Backstreet Boys, Nick Carter, Howie Dorough, Brian Littrell, and Kevin Richardson were in attendance. On November 27, 2012, the couple welcomed their first child, a daughter named Ava Jaymes. On September 5, 2016, McLean announced on Instagram that his wife was pregnant with their second child, another girl. On March 19, 2017, the couple's second child, whom they named Lyric Dean, was born in Los Angeles.

As of June 2012, McLean was working on his second solo album. He also posted two of his new songs on Socialcam on July 23, 2012, titled "Peach" and "P.L.A.R.S."

McLean also appeared and performed with the Backstreet Boys on Arthur, Sesame Street, Sabrina the Teenage Witch, and Saturday Night Live. In 2013, McLean made his motion picture debut by appearing in the comedy, This Is the End, along with the rest of the Backstreet Boys.

On July 22, 2015, McLean launched Skulleeroz Vapor, a line of liquids for use with electronic cigarettes.

McLean was set to release his second solo album titled Naked on September 9, 2016. The lead single, "Live Together" was released on September 4, 2015, on iTunes.