Mike, a bass guitarist and vocalist, worked at the Beatles' "Apple Studios", where his love for music grew stronger after some memorable sessions with several famous singers. He also joined a band, "Gold", who, despite having few hits, sold a number of singles such as "Stay with Me My Love" and "Paradise".
At some point O'Donnell and Junior Campbell signed to the same publisher, and their partnership sparked. They have collaborated on writing television jingles, which continued even after leaving their bands.
O'Donnell lives in Surrey with his wife Barbera, daughter Sian and son Ben.