Christadelphians are consistently pacifist: they refuse to participate in military service on the grounds that Christians should not kill, that the kingdom of God — not any earthly nation — deserves their ultimate allegiance, and that Christ's teaching on non-violence (Matthew 5:38-48) prohibits bearing arms. During both World Wars, Christadelphians in Britain and other countries registered as conscientious objectors rather than serving in the military.

This pacifist stance is grounded in the Christadelphian understanding of the relationship between the church and the state. Christadelphians regard themselves as 'aliens and strangers' in the world — citizens of the coming kingdom of God rather than committed participants in earthly political and military enterprises. Pledging allegiance to earthly nations and their wars is considered incompatible with the higher allegiance owed to God and his coming kingdom.

Christadelphians have historically been willing to serve in non-combatant roles — working in hospitals, agriculture, or other forms of alternative service — as an expression of their willingness to serve the community without bearing arms. Their pacifism is not an expression of political ideology but of eschatological conviction: the kingdoms of this world belong to the age that is passing away, and the Christadelphian's energies are devoted to the coming kingdom of God.