Mark Milne, Sandy McIntosh and Tim Potocic, all members of the band Tristan Psionic, launched Sonic Unyon Records in 1993. Still in university at the time, Sandy and Mark began organizing shows and dubbing tapes for their band and other locals. When the pair took on Tim as Tristan Psionic’s new drummer, they had unknowingly found the final partner for business that would last much longer than first anticipated. Today Mark and Tim continue to run Sonic Unyon and its various offshoot businesses, while Sandy is now a practicing architect.

Over the years, Sonic Unyon has branched out in numerous ways. 

Sonic Unyon Distribution was founded in 1998 to distribute Sonic Unyon and other labels in Canada, amassing a roster that included dozens of domestic imprints (including Alien 8, BattleAxe, Constellation, Meter, Noise Factory, and Sappy Records) as well as exclusively representing over 200 international independent labels in Canada (including Amphetamine Reptile, Darla, Dischord, Epitaph, Fat Wreck Chords, Jagjaguwar, Matador, Merge, Metalheadz, Nuclear Blast, Secretly Canadian, Southern, Thrill Jockey, and Warp). Sonic Unyon also ran hardcore label Goodfellow Records and the more mainstream imprint Labworks. Sonic Unyon Distribution was ultimately sold to MapleCore in 2008.

In 2009, Sonic Unyon became the organizing force behind Hamilton's free music and arts festival Supercrawl, growing it from 3,000 attendees in the first year to 250,000 by 2018 and closing down blocks of downtown Hamilton in order to host hundreds of artists, including the likes of Broken Social Scene, Lights, Arkells, Monster Truck, Sharon Jones and the Dap Kings, Charles Bradley, Yo La Tengo, and Spoon. Supercrawl also presents ticketed concert events throughout the year.  Sonic Unyon has since broadened its events-based business to include the annual Because Beer Craft Beer Festival, and the opening of their own multi-use cultural events space Mills Hardware — in addition to being the force behind JUNOfest 2015 and Hamilton's Pan Am Games closing events.

By 2014, Sonic Unyon Records left behind its music distribution business completely. The label is now distributed domestically by Universal Music Canada and internationally by The Orchard, and its contemporary signings — artists such as Terra LightfootBasement Revolver, and Sam Weber — are making a strong case for another 25 years of great independent music.

In 2019, the label released Sonic Unyon: Now We Are 25, a limited-edition triple-LP celebration of its vibrant catalogue, as well as a feature-length documentary detailing Sonic Unyon Records' storied history. Alongside these releases, the label also marked its 25th anniversary by teaming up with Hamilton's Jillard Guitars on The 99 James North Project — a unique, limited edition run of 25 hand-crafted custom guitars made from wood reclaimed during the meticulous restoration of 99 James Street North, a four-storey Victorian that was brought back to life in 2015. Proceeds from the project are being donated to Hamilton-based charity An Instrument For Every Child.