Scaggs was born William Royce Scaggs in Canton, Ohio, the son of a traveling salesman. The family moved to Oklahoma, then to Plano, at that time a Texas farm town just north of Dallas. He attended a Dallas private school, St. Mark's, where a schoolmate gave him the nickname "Bosley". This was later shortened to Boz.

After learning guitar at the age of 12, he met Steve Miller at St. Mark's. In 1959, he became the vocalist for Miller's band, The Marksmen. The pair later attended the University of Wisconsin–Madison together, playing in blues bands like The Ardells and The Fabulous Knight Trains.

Leaving school, Scaggs briefly joined the burgeoning rhythm and blues scene in London. After singing in bands such as The Wigs and Mother Earth, he traveled to Sweden as a solo performer, and in 1965 recorded his solo debut album, Boz, which was not a commercial success. Scaggs also had a brief stint with the band The Other Side with Mac MacLeod and fellow American Jack Downing.

Returning to the U.S., Scaggs promptly headed for the booming psychedelic music center of San Francisco in 1967. Linking up with Steve Miller again, he appeared on the Steve Miller Band's first two albums, Children of the Future and Sailor. After being spotted by Rolling Stone publisher Jann Wenner, Scaggs secured a solo contract with Atlantic Records in 1968.[citation needed]

Despite good reviews, his sole Atlantic album, Boz Scaggs, featuring the Muscle Shoals Rhythm Section and slide guitarist Duane Allman, performing Fenton Robinson's "Loan Me A Dime", achieved moderate sales, as did follow-up albums on Columbia Records. (His Atlantic album was deleted and replaced with the exact same cover and tracks, but it was given a new catalog number and it was completely remixed in Los Angeles in 1977. This new remix brought Duane Allman's guitar up to the front, but it greatly altered the original feeling. On the track "Finding Her", the volume faded down low for the last minute, an obvious mixing error by engineer Craymore Stevens. The original has never been available on CD.)[citation needed]

In 1976, he linked up with session musicians who would later form Toto and recorded his smash album Silk Degrees. The album reached #2 on the US Billboard 200, and #1 in a number of countries across the world, spawning three hit singles: "Lowdown", "Lido Shuffle", and "What Can I Say", as well as the MOR standard "We're All Alone", later recorded by Rita Coolidge and Frankie Valli. A sellout world tour followed, but his follow-up album, the 1977 Down Two Then Left, did not fare as well commercially as Silk Degrees.

The 1980 album Middle Man spawned two top 20 hits, "Breakdown Dead Ahead" and "Jojo," and Scaggs enjoyed two more hits in 1980-81 ("Look What You've Done to Me" from the Urban Cowboy soundtrack, and "Miss Sun" from a greatest hits set, both U.S. #14 hits). But Scaggs' lengthy hiatus from the music industry (his next LP, Other Roads, would not appear until 1988) slowed down his chart career dramatically. "Heart of Mine" in 1988, from Other Roads, was Scaggs' final Top 40 hit.

Scaggs continued to record and tour sporadically throughout the 1980s and 1990s, and for a time was semi-retired from the music industry. He opened the San Francisco nightclub, Slim's, in 1988, and remains a co-owner as of 2008.

After Other Roads, Scaggs took another hiatus and then came back with Some Change in 1994. He released Come On Home, an album of blues, and My Time, an anthology in the late 1990s. He garnered good reviews with Dig although the CD, which was released on September 11, 2001, was lost in the post-9/11 melée. In May 2003, Scaggs released But Beautiful, a collection of jazz standards that debuted at #1 on the jazz chart.

He tours each summer, has a loyal cadre of fans, remains popular in Japan, and released a DVD and a live CD in 2004. Other releases followed. In 2008, Scaggs undertook an expanded tour across the US.