Was Jesus a Martyr?

I would strongly suggest that the term 'martyr' should not be used to describe Jesus.

"Why cannot Christ be called a martyr? Because he was not a witness to truth but was 'the truth', and his death was not a martyrdom but the Atonement."

— Søren Kierkegaard

 In the 3rd chapter of The Cross of Christ (pp. 87 – 92) John Stott contrasts Jesus' agony in Gethsemane with the joy of Christian martyrs of being counted worthy to die for God and anticipating being united with him. He concludes that if Jesus was distraught about undergoing mere physical suffering, then he would be the most cowardly of all the martyrs. Therefore, what Jesus was distressed about was the spiritual suffering he was about to undergo — the wrath of God, that is, being utterly cut off from him. This kind of suffering no martyr has ever or will ever have to undergo. No Christian martyr need ever cry "My God, my God, why have you forsaken me?"

Martyrs are killed by men because of their convictions (they believe in Jesus); they die as witnesses to the truth. Jesus was also killed because of his convictions (he believed he was God), but ultimately he did not die as a mere witness at the hands of men — he died for our sins at the hand of God! He not only physically suffered and died, but spiritually suffered and died. Separation from God is the essence of spiritual death. Martyrs rejoice in God being with them in their suffering, but the essence of Jesus' suffering was God not being with him.

It is impossible to know the suffering that Jesus underwent on the cross.