Whether secular humanism counts as a religion is a live dispute, and unusually, both the people who say yes and the people who say no have practical reasons for their answer rather than merely definitional ones.
The argument has a legal centre of gravity in the United States. In Torcaso v. Watkins (1961), striking down a state requirement that officeholders declare a belief in God, the Supreme Court remarked in a footnote that among religions in the country not teaching a belief in God were Buddhism, Taoism, Ethical Culture, Secular Humanism and others. The footnote was incidental to the ruling and settled nothing, but it has been quoted ever since by religious conservatives arguing that public schools, by teaching a curriculum without God, are establishing secular humanism as a state religion in breach of the First Amendment. Courts have not accepted the conclusion, but the argument recurs.
Humanists themselves are divided. Some accept a functional definition and are content with it: a movement with ceremonies, communities, pastoral care and a life stance is doing much of what religions do, and the legal parity that follows is worth having, since it brings equal access to chaplaincy, broadcasting time, school provision and charitable status. Others reject the label outright, on the ground that humanism makes no supernatural claim and that accepting the word invites exactly the confusion the movement exists to clear up.
Jurisdictions outside the United States have mostly sidestepped the question by widening the category instead of arguing about the boundary. British law protects religion or belief together, and philosophical convictions including humanism qualify. The European Court of Human Rights held in Kokkinakis v. Greece (1993) that freedom of thought, conscience and religion is a precious asset for atheists, agnostics and sceptics as much as for believers. On that approach it does not matter whether humanism is a religion, because the protection does not depend on the answer.