David Drew, 64, told an employment tribunal that Walsall Manor Hospital made him feel like a 'religious maniac' for sending the message.
The father of four insisted he emailed the prayer, by 16th century Jesuit founder St Ignatius Loyola, to motivate his department.
He prefaced it by saying: 'I find this a personal inspiration in my frail imperfect efforts to serve my patients, their families and our department.'
But one staff member found his emails 'strange' and another 'bizarre and inappropriate', the Birmingham tribunal heard.
Dr Drew, a Baptist churchgoer of Sutton Coldfield, rose to become clinical director at the hospital. But he was dismissed for 'gross misconduct and insubordination' in December 2010 and lost an initial appeal last April.
An internal review of the complaints against him concluded his religious language was inappropriate in a professional setting.
Judge David Kearsley said Dr Drew should have avoided talking about religion if it was considered 'inappropriate' or hindered 'proper communication'.
The doctor said last night the ruling means people could no longer say 'I am a Christian' in the workplace. He plans to appeal.