He works out of the small town of Anacortes in northern Washington state and has released more than three-dozen recordings under his own name. He is part of the Knw-Yr-Own label collective, but has also issued titles on K and Marriage Records. Many of his albums have appeared as individually designed cassettes and CD-Rs of homemade four-track recordings that were individually mailed to subscribers of his Kelp! Monthly or Kelp Lunacy Advanced Plagiarism Society (aka KLAPS) labels. Additionally, Blau is an in-demand session and touring musician. He has worked extensively with Laura Veirs, but his résumé includes recordings and tours with the Microphones, LAKE, Earth, and Mount Analog, to name a scant few. He is a founding member of D+, Your Heart Breaks, Captain Fathom, Les Hauts Sommets, Lovers Without Borders, and the Bundles.

Blau's own music is wildly diverse. Usually classified as an "indie rock" musician, it proves a woefully inadequate categorization. Blau's sounds include grafting folk and country-rock onto hazy blues, rocksteady reggae, '70s soul harmonies, and ceremonial-sounding flutes, bossa nova, dub, and experimental drone in an unpredictable, shape-shifting mixture of elements.

His first two releases, Doin' Things the Way They Happen and Blue Nomad, appeared as cassettes in 1996 on Knw-Yr-Own. They were followed by the acclaimed Shell Collection (a compilation of four-track sessions) in 1997. Due to his kaleidoscopic versatility, the album stood in sharp contrast to virtually everything else on the lo-fi indie underground at the time.

After a split self-titled outing with Tippy Young on Dead Turtle Recordings, Blau started issuing his KELP! Monthly albums in 2003 and through 2006, they appeared with startling regularity (though not strictly monthly). They include Dark, Magic Sea, The Coconutcracker, Dunkel Blau, If I Knew Zen What I Know Now, and Am. Blau's debut for K was 2006's Beneath Waves. He followed it with Dance Positive for Marriage Records in 2007, then returned to K for 2008's Nature's Got Away and 2009's Zebra; 96 and Baby Nettles were self-released the same year. Blau continued to record solo, but over the next several years, he worked with his various bands, toured, and did session work that claimed much of his time. In 2010, the Bundles issued their self-titled debut. In 2011 and 2012, he appeared on both volumes of Earth's Angels of Darkness, Demons of Light albums; he was also a member of the live ensemble, Your Heart Breaks, which released Harsh Tokes & Bong Jokes in 2012. In 2013, he played drums on the Microphones' It Was Hot We Stayed in the Water, and in 2014, he played bass and guitar on Nicholas Krgovich's On Sunset. That same year he released Maherican Dream on KLAPS, and reprised his roles on Krgovich's The Hills ‎a year later.

Back in 2004, producer Tucker Martine (My Morning Jacket, Bill Frisell, the Decemberists, Jenny Scheinman) and Blau recorded a cover single (as Mount Analog) of Tom T. Hall's nugget "That's How I Got to Memphis." The collaboration proved mutually satisfying, and the pair discussed cutting an entire album together. It took over a decade for their project to come to fruition. In 2016, Editions Mego released Introducing Karl Blau, a covers collection done in a 21st century cosmic-country style. It included songs composed by the Bee Gees, Link Wray, Townes Van Zandt, and Layng Martine, Jr. (Tucker's father). ~ Thom Jurek