The argument from morality is an argument for the existence of God. Arguments from morality tend to be based on moral normativity or moral order. Arguments from moral normativity observe some aspect of morality and argue that God is the best or only explanation for this, concluding that God must exist. Arguments from moral order are based on the asserted need for moral order to exist in the universe. They claim that, for this moral order to exist, God must exist to support it. The argument from morality is noteworthy in that one cannot evaluate the soundness of the argument without attending to almost every important philosophical issue in meta-ethics.

German philosopher Immanuel Kant devised an argument from morality based on practical reason. Kant argued that the goal of humanity is to achieve perfect happiness and virtue (the summum bonum) and believed that an afterlife must be assumed to exist in order for this to be possible, and that God must be assumed to exist to provide this. Rather than aiming to prove the existence of God, however, Kant was simply attempting to demonstrate that all moral thought requires the assumption that God exists, and therefore that we are entitled to make such an assumption only as a regulative principle rather than a constitutive principle (meaning that such a principle can guide our actions, but it does not provide knowledge). In his book Mere Christianity, C. S. Lewis argued that "conscience reveals to us a moral law whose source cannot be found in the natural world, thus pointing to a supernatural Lawgiver." Lewis argued that accepting the validity of human reason as a given must include accepting the validity of practical reason, which could not be valid without reference to a higher cosmic moral order which could not exist without a God to create and/or establish it. A related argument is from conscience; John Henry Newman argued that the conscience supports the claim that objective moral truths exist because it drives people to act morally even when it is not in their own interest. Newman argued that, because the conscience suggests the existence of objective moral truths, God must exist to give authority to these truths.

Contemporary defenders of the argument from morality are Graham Ward, Alister McGrath and William Lane Craig.

All variations of the argument from morality begin with an observation about moral thought or experiences and conclude with the existence of God. Some of these arguments propose moral facts which they claim evident through human experience, arguing that God is the best explanation for these. Other versions describe some end which humans should strive to attain that is only possible if God exists.

Many arguments from morality are based on moral normativity, which suggests that objective moral truths exist and require God's existence to give them authority. Often, they consider that morality seems to be binding – obligations are seen to convey more than just a preference, but imply that the obligation will stand, regardless of other factors or interests. For morality to be binding, God must exist. In its most general form, the argument from moral normativity is:

Some arguments from moral order suggest that morality is based on rationality and that this can only be the case if there is a moral order in the universe. The arguments propose that only the existence of God as orthodoxly conceived could support the existence of moral order in the universe, so God must exist. Alternative arguments from moral order have proposed that we have an obligation to attain the perfect good of both happiness and moral virtue. They attest that whatever we are obliged to do must be possible, and achieving the perfect good of both happiness and moral virtue is only possible if a natural moral order exists. A natural moral order requires the existence of God as orthodoxly conceived, so God must exist.

In his Critique of Pure Reason, German philosopher Immanuel Kant stated that no successful argument for God's existence arises from reason alone. In his Critique of Practical Reason he went on to argue that, despite the failure of these arguments, morality requires that God's existence is assumed, owing to practical reason. Rather than proving the existence of God, Kant was attempting to demonstrate that all moral thought requires the assumption that God exists. Kant argued that humans are obliged to bring about the summum bonum: the two central aims of moral virtue and happiness, where happiness arises out of virtue. As ought implies can, Kant argued, it must be possible for the summum bonum to be achieved. He accepted that it is not within the power of humans to bring the summum bonum about, because we cannot ensure that virtue always leads to happiness, so there must be a higher power who has the power to create an afterlife where virtue can be rewarded by happiness.

Philosopher G. H. R. Parkinson notes a common objection to Kant's argument: that what ought to be done does not necessarily entail that it is possible. He also argues that alternative conceptions of morality exist which do not rely on the assumptions that Kant makes – he cites utilitarianism as an example which does not require the summum bonum. Nicholas Everitt argues that much moral guidance is unattainable, such as the Biblical command to be Christ-like. He proposes that Kant's first two premises only entail that we must try to achieve the perfect good, not that it is actually attainable.