Panagiotis Andreou was born June 3, 1978, in Athens, Greece, and grew up between two very different musical households: a father whose side of the family favored working-class bouzouki music, and a mother, unusually modern for her generation in Greece, who filled the house with Beatles and Motown records. He began formal training on baroque recorder at a young age, playing alto and bass recorder for about a decade, then continued at a public Greek music high school that combined a standard academic day with several additional hours of classical and Byzantine music instruction, where he studied classical piano and clarinet. He picked up electric bass as a teenager after watching someone play it, moving quickly from heavy metal and Bon Jovi covers into Motown, and then, after a bandleader returned from Cuba with a stack of salsa records, into Afro-Cuban music, which became the foundation of his rhythmic vocabulary. Through the 1990s he worked Athens's active live-music scene, playing salsa, Latin jazz, and Balkan and Greek folkloric styles in clubs that booked bands nightly.

In 1999 Andreou enrolled at Berklee College of Music, and he later earned a master's degree from the jazz program at the State University of New York at Purchase, settling in New York in the process. He became a founding member of the Afro-Cuban-styled ensemble Gonzalo Grau y La Clave Secreta in 2001; its 2008 album Frutero Moderno, on which Andreou plays bass and sings lead and backing vocals, was nominated for Best Tropical Latin Album at the 51st Annual Grammy Awards. He was also a founding member of the New York Gypsy All-Stars, a Balkan- and Middle Eastern-rooted band built around clarinetist Ismail Lumanovski and kanun player Tamer Pınarbaşı that plays regularly at the Manhattan club Drom and tours internationally on the jazz, classical, and Gypsy-festival circuit; Andreou plays bass throughout the group's 2011 album Romantech (Traditional Crossroads), which also features keyboardist Jason Lindner.

Andreou's most prominent association began in Brooklyn in 2006, when Lindner formed an electric band initially built around a quintet, with Andreou on electric bass, Mark Guiliana on drums, and MC/beatboxer Baba Israel, before settling into the trio Now Vs Now. Meshell Ndegeocello, in whose band Lindner had played for several years, produced and named the group's self-titled debut, released in 2009 on Anat Cohen's label, Anzic Records. Andreou plays electric bass, and sings on several tracks, across all ten songs on that album, which also carries guest appearances from Anat Cohen (tenor saxophone and pandeiro on "Ahimsa"), trumpeter Avishai Cohen, guitarist Kurt Rosenwinkel, percussionist Yosvany Terry, vocalist and conguero Pedrito Martinez, and vocalist Claudia Acuña. Now Vs Now continued with Earth Analog (2013, largely composed from Andreou and Lindner's laptop sketches) and The Buffering Cocoon (2018, Jazzland Recordings), the latter recorded with Justin Tyson on drums after Guiliana's departure; Andreou has remained the trio's bassist across every lineup since its founding.

In 2010 the Latin Jazz Corner blog named Andreou its "Latin Bass Player of the Year." He has continued to work across genres as a bandleader, sideman, and touring musician: he formed the Greek band Syn...Phonia, in which he also sang, and the trio Morning Bound in 2014; recorded with flautist Mark Weinstein on Timbasa (2011), the Ivan Milev Band, guitarist Davide Tammaro, saxophonist Chris Frangou, vocalist Maria Manousaki, and pianist Giorgi Mikadze; and toured internationally backing the Ethiopian bandleader Mulatu Astatke alongside Lindner and drummer Marcus Gilmore. In 2026 Andreou appeared as a featured sideman on Israeli bassist and guitarist Tal Mashiach's second album, Who's Around? (Anzic Records), playing bass and singing alongside a seventeen-musician ensemble that again included Anat Cohen on clarinet; Andreou is credited as a featured performer on the track "Creta."

Andreou describes himself, half-joking, as not "a jazz guy," despite training in two jazz programs and building a career largely among jazz musicians; what he means is that his vocabulary comes less from the American jazz songbook than from a deliberate fusion of traditions he absorbed directly: Afro-Cuban clave and timba, Greek and Balkan folk meters and modal melody, funk, and South Indian Konnakol vocal percussion, which he layers rhythmically over his own bass lines. That range is what makes him, in the description of one interviewer, "the bassist of choice for forward-thinking, genre-busting groups" - the same instrumentalist equally at home holding down Now Vs Now's electronic-jazz groove, driving the New York Gypsy All-Stars' odd-metered Balkan themes, and singing lead in Spanish-language salsa with Gonzalo Grau y La Clave Secreta.