- O’Callaghan, John & Howells, Sarah
- O’Callaghan, John & Larkin, Betsie
- O’Callaghan, John & McLaughlin, Deirdre
- O’Callaghan, John & Stagg, Clare
- O’Callaghan, John feat. Gallagher, Audrey
- O’Callaghan, John feat. Howells, Sarah
- O’Callaghan, John Feat. Jaren
- O’Callaghan, John feat. Jaren
- O’Callaghan, John Feat. Josie
- O’Callaghan, John feat. Josie
- O’Callaghan, John feat. Larkin, Betsie
- O’Callaghan, John Feat. Ria
- O’Callaghan, John feat. Ria
- O’Callaghan, John featuring Ria
- O’Connell, Helen
- O’Connell, Lauren
- O’Connell, Maura
- O’Connell, Robbie
- O’Connor (Argentine hard rock band)
- O’Connor, Caroline
- O’Connor, Caroline & Bolton, John
- O’Connor, Des (English singer, lyricist)
- O’Connor, Donald
- O’Connor, Jennifer
- O’Connor, Mark (US bluegrass, country and classical fiddler/composer)
- O’Connor, Maz
- O’Connor, Paddy
- O’Connor, Sinéad
- O’Connor, Sinéad feat. Blockheads, The
- O’Connor, Sinéad feat. U2
- O’Day, Alan
- O’Day, Anita
- O’Day, Anita & Krupa, Gene
- O’Day, Anita & Three Sounds, The
- O’Day, Anita & Tjader, Cal
- O’Day, Anita with May, Billy
- O’Day, Molly (American country music vocalist)
- O’Death
- O’Dell, Kenny
- O’Dette, Paul (American conductor and lute player specialising in early music)
- O’Donis, Colby
- O’Donis, Colby feat. Akon
- O’Donnell, Daniel
- O’Donnell, Daniel & Duff, Mary
- O’Donnell, Erin
- O’Donnell, Martin & Salvatori, Michael
- O’Donnell, Martin & Salvatori, Michael
- O’Donnell, Martin and Salvatori, Michael
- O’Donnell, Rosie
- O’Donnell, Ryan & Rachel
- O’Donovan, Aoife
- O’Dowda, David
- O’Dwyer, Áine
- O’Farrill, Chico
- O’Flynn (London DJ and producer)
- O’Flynn, Liam
- O’G3NE (formerly “Lisa, Amy & Shelley”)
- O’Halloran, Dustin
- O’Halloran, Dustin & Gyða Valtýsdóttir
- O’Halloran, Dustin & Senti, Bryan
- O’Halloran, Dustin & Siggi String Quartet
- O’Halloran, Dustin, ACME String Quartet
- O’Hara, Catherine
- O’Hara, Jamie
- O’Hara, Jill
- O’Hara, Kelli
- O’Hara, Mary
- O’Hara, Mary Margaret
- O’Hara, Paige
- O’Hara, Paige, White, Richard and Chorus
- O’Hearn, Patrick (American bass guitarist and keyboardist)
- O’Hora, Ronan, Royal Philharmonic Orchestra, Carney, Jonathan
- O’Jays, The
- O’Kanes, The
- O’Kaysions, The
- O’Keefe Music Foundation (Music School)
- O’Keefe, Danny
- O’Keefe, Johnny
- O’Keefe, Laurence & Benjamin, Nell
- O’Malley, Katie
- O’Meara, Jo
- O’My’s, The (Chicago rock/soul duo)
- O’Neal, Alexander
- O’Neal, Alexander feat. Cherrelle
- O’Neal, Shaquille (performs as DJ Diesel aka Diesel)
- O’Neal, Shaquille feat. RZA & Method Man
- O’Neil, Melissa
- O’Neill, Sharon
- O’Neill, Terry (Irish balladeer, "A Nation Once Again" among others)
- O’Quin, Greg
