[3] After sitting in with the Stooges on several occasions, he formally joined the group at the behest of lead singer Iggy Pop[3] two days before they left Detroit for Los Angeles to record Fun House in May 1970.

[7] Throughout the 1970s and 1980s, Mackay played and recorded with a highly diverse cross-section of underground musicians, including Violent Femmes,[2] Snakefinger,[3] Commander Cody,[3] Smegma, Zu, Andre Williams, the Moonlighters, Clubfoot Orchestra, and Van Rozay from San Jose, California.

He was based in Ann Arbor (where he continued to work at Discount Records and perform with Carnal Kitchen and the Mojo Boogie Band, a blues rock ensemble) until 1976, when he initially relocated to the San Francisco Bay Area.

In 2000, Stooges biography pages on websites for MTV, VH1, and Rolling Stone included an item indicating that Mackay had died as a result of a heroin overdose in the 1970s.

According to Alexis Petridis, "Kent had apparently misheard the lyrics of Iggy Pop's 'Dum Dum Boys,' which mentioned the death of Stooges roadie and bassist Thomas 'Zeke' Zettner.

The first full-scale tour of Steve Mackay and the Radon Ensemble was mounted in July 2003; with a percussion-heavy lineup that featured bassist Marlon Kasberg (Liquorball), drummer Sam Lohman (Nimrod 36), multi-instrumentalist Travis McAlister (Nequaquam Vacuum), scrap percussionist and vocalist Noah Mickens (also Nequaquam Vacuum), and drummer and band leader Scott Nydegger (Sikhara).

Other musicians who have performed and recorded with the Radon Ensemble since then included the multi-instrumentalist Tyler Armstrong, projectionist Ed Cooper, bassist Giovanni Donadini, Nyko Esterle, multi-instrumentalists Kamil Kruta of Koonda Holaa and Dan Kauffman, bassist Jason LaFarge, saxophonist Vinnie Paternostro, Fabrizio Modonese-Polumbo, saxophonist Shane Pringle, Frank Pullen, Suzanne Thorpe (Mercury Rev), John Wiese (Bastard Noise), and drummer Ed Wilcox.

In December 2007, Mackay recorded two day sessions at the Big Baldy's Toe studio in Claremont CA, home to Amps for Man Is the Bastard founder Henry Barnes.

In 2009 Iggy Pop contributed his version of vocals to the track and subsequently it was used in a French movie L'Étoile du jour (Morning Star) directed by Sophie Blondy.

In 2015, Mackay, lo-fi pioneer R. Stevie Moore and Scott Nydegger (Sikhara) were featured on Shanghai-based experimental punk band Round Eye's eponymous LP, which was released by Florida label Ripping Records.