Lionel Theunissen was born in Brisbane, Australia. He commenced vocal studies at the Queensland Conservatorium of Music in 1991, studying with the renowned Australian tenor, Donald Smith OBE, and continued his studies with Joseph Ward OBE, completing a Bachelor of Music (Voice) degree in 1995. His Conservatorium awards include the Lewis B.J. Reid prize for 1991, the Donald Penman prize for voices in combination for 1992, the Victoria League Betty Fadden bursary for 1993, and the Italian Lyric Diction prize for 1994. He was a finalist in the 1995 and 1996 Shell Covent Garden Scholarships, and won the Bathurst Singer of the Year Competition in 1996, and the Brisbane Musical Theatre competition in 1998 and 2000.
Lionelís roles include Mr. Redburn in the Australian premiere of Benjamin Brittenís Billy Budd, Frilly in Snugglepot and Cuddlepie – The Musical, Dulcamara in Líelisir díamore, Michele in Pucciniís II Tabarro, Javert in Les Miserables, the title roles in Jekyll and Hyde, Fred/Petruchio in Kiss Me Kate, Cinderellaís Prince/Wolf in Sondheimís Into the Woods, and Sir Dennis Galahad in the Brisbane premiere season of Spamalot.
In 2010 and 2011 he played Pilate in Harvest Rainís critically acclaimed production of Jesus Christ Superstar. In 2013 he played the title role in the Queensland community theatre premiere of The Phantom of the Opera. Most recently he played the title role in Spotlight Theatreís production of Sweeney Todd for which he won Best Actor in a Leading Role at the 2014 Gold Coast Area Theatre Awards.