He also tutored and coached at the Guildhall School of Music and Drama where his students included Ewan McGregor, Daniel Craig and Damian Lewis.
While still in school, at the age of fourteen in 1955, he was chosen after an audition to play a young crime victim on an early episode of BBC TV's Dixon of Dock Green.
His first professional stage performance came in 1964 as a member of the Bristol Old Vic repertory company when he appeared in the play Bartholomew Fair followed by dozens of ensemble productions over the next few years.
The decade ended with McCormack playing Borachio in Much Ado About Nothing in a Royal Shakespeare Company UK tour that started in the Autumn of 1979 and continued over into the spring of 1980.
The 1990s started with McCormack taking a starring role as gang member Dolin in the stage production of A Clockwork Orange at the Barbican Theatre.
In 1991 he took a leading role in Griselda Gambaro's Putting Two and Two Together again at the Theatre Upstairs and starred in the 1992 production of Timberlake Wertenbaker's unusual play Three Birds Alighting in a Field.
Throughout his stage and television career McCormack still found time to cultivate a lifelong interest, expertise and extensive knowledge in historic churches and medieval architecture.
In late 2003 McCormack was playing Lord Capulet in a tour of Hong Kong with the Royal Shakespeare Company's Romeo and Juliet when he first started to feel unwell.