He spent his pre-teen years in Jacksonville, Florida, and later lived in Atlanta, Georgia, where he attended Marist High School. Hasselhoff made his theatrical debut at age seven in Peter Pan, and ever since his childhood dream was to have a career on Broadway. He graduated from Lyons Township High School in La Grange, Illinois in 1970. He was a member of the speech team, senior discussion Leaders, President of the choir, captain of the volleyball team and held roles in several plays (including one lead role as Matt in The Fantasticks). He studied at Oakland University before graduating with a degree in theater at the California Institute of the Arts.

Hasselhoff portrayed Dr. "Snapper Foster" on The Young and the Restless from 1975–82, leaving the series as the show wrote out many of their original characters. In 1979, he played "Simon" in Starcrash. He launched his singing career with guest appearances on the first season of children's program Kids Incorporated, performing "Do You Love Me". He guest starred on two episodes of Diff'rent Strokes and the soap opera Santa Barbara as himself in 1984.

His music career took off in the late 1980s and achieved success at the tops of the charts, with his album Looking for Freedom which went triple platinum in Europe. He had one #1 hit in the German pop charts in spring of 1989 ("Looking for Freedom"). He was noted for his performance of the single at the Berlin Wall on New Year's Eve 1989, two months after the East German government had opened the wall, but nine months before unification took place. Wearing a piano-keyboard scarf and a leather jacket covered in motion Lights, Hasselhoff stood in a bucket crane and performed the song along with the crowd. The performance has had a lasting impact on German pop-culture with Hasselhoff commenting that the song became an "anthem" and "song of hope" for the people of East Germany. In 2004, Hasselhoff lamented the lack of a photo of him in the Checkpoint Charlie Museum in Berlin.

Hasselhoff was recruited by then NBC President Brandon Tartikoff to star in the science-fiction series Knight Rider from 1982 to 1986 as Michael Knight. He has described Knight Rider as more than a TV show: "It's a phenomenon. It's bigger than Baywatch ever was." On the success of Knight Rider – "It's because it was about saving lives, not taking lives, and it was how one man really can make a difference. And we had a blast making it, and we made sure nobody died on the show; [just as] we made sure nobody ever drowned on Baywatch". (However, characters did die in a few episodes, including "Knight Of The Phoenix" (the two-hour pilot episode), "Nobody Does It Better" and "Short Notice".)

Hasselhoff was married to Actress Catherine Hickland from March 24, 1984, to March 1, 1989. Their wedding was recreated in the Knight Rider Season 4 episode "The Scent of Roses" which first aired on January 3, 1986.

Hasselhoff returned to television on Baywatch which premiered in 1989. Although it was canceled after only one season, he believed the series had potential, so Hasselhoff revived it for the first-run syndication market in 1991, investing his own money and additionally functioning as executive Producer. His contract stipulated royalties to be paid to him from the rerun profits, which gave him the financial liberty to buy back the rights to Baywatch from NBC.

Hasselhoff married Actress Pamela Bach in December 1989. The couple have two daughters: Taylor Ann Hasselhoff, born May 5, 1990, who attended the University of Arizona and was cast for the 2015 season of Rich Kids of Beverly Hills, and Actress Hayley Hasselhoff, born August 28, 1992. In January 2006, Hasselhoff announced he was filing for divorce, citing irreconcilable differences. Their divorce was finalized in August 2006. Bach was given custody of one daughter and Hasselhoff custody of the other, until Hasselhoff later obtained custody of both. As of December 2010 he resided in Southern California with his daughters, five dogs, and other pets.

In 1991, Hasselhoff reprised his role as Michael Knight in the television film Knight Rider 2000 as a sequel to the original series. The movie served as a pilot for a proposed new series, but despite high ratings, the plan was abandoned.

In 1993, he released the single "Pingu Dance" based on the children's show Pingu. In 1994, he was scheduled to perform a concert on pay-per-view from Atlantic City. The concert was expected to help reignite his singing career in the United States. However, on the night of the concert, O. J. Simpson was involved in a police chase in southern California. Viewership of the concert was significantly lower than expected due to the live coverage of the chase, and the event was ultimately a $1.5 million loss.

In 2000, he made his Broadway debut in the musical Jekyll & Hyde. Following his debut, he starred in other musicals including Chicago and The Producers.

Hasselhoff has made several self-parodic appearances in movies. He had a major role in The SpongeBob SquarePants Movie, released November 19, 2004, starring as himself (though resembling his bygone Baywatch character) and meeting SpongeBob and Patrick (his full name is heard once in the movie; he is referred to as "Hasselhoff"). Hasselhoff also had another short appearance in the movie DodgeBall: A True Underdog Story as the dodgeball coach to the German national dodgeball team, Team Hasselhoff. Berating his team after being eliminated from a tournament, he shouts "Ihr seid alle Schweine!" (translated: "You are all pigs!", a Common German insult) and smashes a photo of himself in his Baywatch attire. In 2004's EuroTrip, Hasselhoff appears in a washroom. In the 2006 Adam Sandler film Click Hasselhoff portrays Sandler's despicable boss. Hasselhoff also appears in an episode of Wildboyz. In 2007, he again played himself in the Jamie Kennedy comedy Kickin' It Old Skool.

Hasselhoff's autobiography Making Waves was released in the United Kingdom in September 2006. In an interview in April 2006, he promised the book would present the "last chapter" regarding controversial elements of his personal life.

On May 3, 2007, a viral video surfaced online of Hasselhoff appearing to be severely drunk inside his home. His daughter, Taylor Ann, who shot the video, can be heard interrogating him and asking him to cease abusing alcohol. She also warns her father he could be jeopardizing his spot on the Las Vegas production of The Producers he starred in at the time. In the wake of the leaked clip, Hasselhoff issued a statement saying it was recorded by Taylor Ann so that he could see how he behaved while intoxicated and the footage was deliberately released. As a result of the video, Hasselhoff's visitation rights with his two daughters were suspended on May 7, 2007, for two weeks until the video's authenticity and distributor were determined. In May 2009, Hasselhoff's attorney, Mel Goldsman, described Hasselhoff as "a recovering alcoholic".

In December 2008, he sang the national anthem at the NCAA Las Vegas Bowl. Although the game was televised live by ESPN, the station chose not to broadcast Hasselhoff's performance.

In September 2009, he featured on a radio podcast for Compare the Meerkat, part of the advertising for British website, Comparethemarket.com. He was the subject of an Early Day Motion in the House of Commons of the United Kingdom as a result of his support for the re-opening of Morecambe Winter Gardens.

On Friday, December 10, 2010, A&E confirmed in a statement that, after airing just two episodes, The Hasselhoffs had been canceled. According to Nielsen Co. ratings, the first episode was seen by 718,000 viewers. Viewers dropped to 505,000 for the second installment, which aired on the same evening. The full series aired in the UK on May 30, 2011, on The Biography Channel.

In 2011, he was a guest judge at the Belgian Idols competition. Hasselhoff became a judge on Britain's Got Talent in 2011 alongside Amanda Holden, Michael McIntyre and Simon Cowell. However, Hasselhoff was axed after only one series on the show. In 2011, he revived his music career with a short tour across Germany, Austria and Switzerland. In the same year, Hasselhoff is featured in the trailer of the spin-off downloadable game, Burnout Crash!. On October 1, 2011, David Hasselhoff attended Knightcon 2011 at Xscape, Castleford, UK, with girlfriend Hayley Roberts. The event was also attended by former Knight Rider cohorts Rebecca Holden (April Curtis in Season 2), Peter Parros (Reginald Cornilius III (RC3) in Season 4), and Michael Scheffe, the designer of KITT. In 2012, he was a contestant on The Celebrity Apprentice Australia . He appeared on '8 out of 10 Cats' on May 11, 2012, and entertained the audience by using the word 'willy'.

Since 2013, Hasselhoff has dated Hayley Roberts, from the town of Glynneath in Wales. He is a fan of Welsh rugby union, and they regularly attend rugby matches in Wales.

On February 24, 2014, he opened his own 10-week talk show in Sweden on TV3, in English. A similar show was later recorded in Finland, premiering on Sub on April 2, 2015.

After touring Glasgow during late 2015, Hasselhoff stated that he supports Scottish football team Partick Thistle F.C..

In 2017 Hasselhoff appeared in short film It's No Game by Director Oscar Sharp, playing "The HoffBot". Hasselhoff's lines were generated by a neural network artificial intelligence (called Benjamin) using a statistical model trained on his own 80's and 90s television performances. Hasselhoff said the A.I. "really had a handle on what's going on in my life and it was strangely emotional".