Galileo Galilei - Gary Adams
Mathematician/Monk/First Secretary/Ballad Singer's Wife - Natasha Agnew
Ludovico Marsili - Stephen Balchin
Sagredo/Infuriated Monk/Ballad Singer - Phil Braithwaite
Philosopher (Rector)/Doge/Fat Prelate/Town Crier - Ken Buddell
First Senator/Cardinal Barberini, later Pope Urban VIII - Basil Clarke
Virginia Galilei - Antoinette di Michele
Cosmo di Medici/Young Girl/Boy - Sarah Fox
Lord Chamberlain/Scholar/Giuseppe/Guard - Andy Grant
Andrea Sarti (as a boy) - Sam Kenny 
Andrea Sarti (as a young man) - Mansoor Mir
Federzoni/Customs Officer - Jennifer Moorby
Priuli/Young Lady/Second Secretary/Informer/Clerk - Salley Rear
Second Senator/Old Cardinal/Inquisitor - Paul Robinson
Matti/Second Monk - Tim Saward
Little Monk - Anthony Townsend
Elderly Lady/Clavius/Cardinal Bellarmin/Peasant - Rosemary Watt-Wyness
Mrs Sarti/Friend - Jackie Withnall