Do I Need Professional Training To Become An Actor?

The simple answer to this is YES and NO.

NO, if you are the most able, capable actor, fully able to dissect scripts of any genre or era, fit, well balanced and coordinated, emotionally available, open, able to relax under pressure, you can sing with the perfect pitch and tone, move as a dancer, with grace, momentum and stop on a penny.  If you can fill two thousand seater theatre night after night after night after night, with your voice (and not be shouting) and not lose your voice.  If you can find your own work and manage your own career.  If you already know lots of directors and work with them regularly so that you know what the daily demands of the working life of an actor are, if you fully skilled in television, radio and film techniques, if you are great working with others and know yourself inside out and have mastered yourself, then NO.

If you haven't quite managed all of this, then YES, you do, if you want to work as a professional actor for life and put food on your table regularly.