Justice Thomas Warren rejected the request by Stephen Lockhart for either a reversal of his conviction, or a new trial.
Lockhart was convicted in 2001 of killing Andrea Lockhart.
Prosecutors proved that he killed her with a piece of lumber at the boatyard in Southwest Harbor where he worked.
He put her body in a box, filled it with spray foam and covered it with fiberglass.
Lockhart says his lawyer was ineffective because he failed to get a psychological evaluation.
Lockhart is currently serving a 47-year sentence.