[1] O'Donnell briefly attended art school but left to pursue a career as a professional musician; his first paying gig was in 1976, backing Arthur Brown.

[7][8] Unhappy with the large stadium-sized shows that the Cure played during that album's tour, and with personal differences among bandmates, O'Donnell left the band for the first time in 1990.

[1] O'Donnell released three solo albums in the following years, including The Truth in Me,[9] and formed a record label called 99X/10 with longtime partner Erin Lang.

[13] Since rejoining the band, he has continued to release solo works regularly,[14] most recently the album 7 Different Words for Love in 2022;[15] he has also composed a classical suite called "Quieter Trees" for orchestral performance.

O'Donnell posted a lengthy thread on X for Blood Cancer Awareness Month, stating: "In September last year I was diagnosed with a very rare and aggressive form of lymphoma.