This article explores Jaco Pastorius’s efforts to legitimize himself as a jazz electric bassist. Even though the instrument had existed at the margins of jazz for decades, by the 1970s it was overwhelmingly associated with rock and funk music and therefore carried with it the stigmatized connotations of outsider status. Building on the work of Bill Milkowski, Kevin Fellezs, Lawrence Wayte, and Peter Dowdall, I situate Pastorius’s career within the broader context of 1970s jazz fusion. I then analyze how he deliberately used his public persona, his virtuosic technical abilities, the atypical timbre of his fretless electric bass, and his work as a composer and bandleader to vie for acceptance within the jazz tradition. As I argue, Pastorius specifically attempted to establish his jazz credibility through his first two solo albums, initially by disassociating himself from his own instrument, and then by eventually abandoning the musical style that had made him famous. Ultimately, Pastorius’s story serves as a useful case study of the tangible ramifications of authenticity disputes and the complicated ways in which musicians have attempted to navigate contested musical spaces within popular music.