Whether or not Mersault is a martyr depends on perspective. In his own eyes Mersault is a martyr for the truth. His passion for the exact truth was the reason for his execution. Initially it appeared that he was just accepting of whatever life brought his way, but by the final chapter he experiences a rapture where he becomes, "sure of myself, sure of everything, surer than he was, sure of my life and sure …showed first 75 words of 997 total…

…showed last 75 words of 997 total…ends once you leave his head. Was Mersault a martyr to his existential beliefs? Yes. He made what he thought were rational decisions despite existing in an irrational universe. He defined his life by only admitting to what he directly experienced. Anything less would have been a lie and therefore not rational. Was he a martyr in the more conventional sense? No. Mersault was just admitting and accepting punishment for a crime he did commit.