|Blanche Fury (1948) [Philip Thorn]: Executed (off-screen) by hanging; we last see him in the execution chamber. (Thanks to Brian)
Young Bess (1953) [Thomas Seymour]: Executed by beheading.
Footsteps in the Fog (1955) [Stephen Lowry]: Poisons himself in an attempt to frame Jean Simmons for attempted murder (expecting that she'll return in time to bring the doctor); he dies shortly after she arrives too late. (Thanks to Brian)
Moonfleet (1955) [Jeremy Fox]: Stabbed in the back by George Sanders; he manages to shoot George in turn, then dies (off-screen) after making his way back to say goodbye to Jon Whiteley and sailing out to sea so that Jon won't learn of his death.
The Wild Geese (1978) [Sir Edward Matherson]: Shot to death by Richard Burton in Stewart's townhouse. (Thanks to Brian and Greg)
Chameleons (1989) [Jason Carr a.k.a. Captain Chameleon]: I vaguely recall that he was murdered early in the movie, though I can't remember the details.