Dear Goaty McSheepson,
No; I doubt that Malthus (1766-1834), a clergyman, would ever have suggested euthanasia. He saw population as limited by war, disease, and famine; and his suggestion for an alternative to that, was a form of moral restraint. Although he viewed birth control as sinful, he thought people could marry later in life, which would lead to fewer children.
He is known primarily as the first economist to propose a systematic theory of population; that population growth happens exponentially, while food supply increases arithmetically. However his work did not include the effects of the Industrial Revolution and many other recent factors.