  We study the construction of a manifestly covariant worldline action from a
coadjoint orbit. A coadjoint orbit is a submanifold in the dual vector space of
the Lie algebra and generated by coadjoint actions. Since a coadjoint orbit is
a symplectic space, we derive the worldline particle action from the symplectic
two-form. One subtlety in formulating worldline particle actions from coadjoint
orbits is choosing the coordinate system that sufficiently illustrates physical
properties of the particles. We introduce Hamiltonian constraints by the
defining conditions of the isometry. This allows us to write a manifestly
covariant worldline action. We demonstrate our method to the both massive and
massless particles in Minkowski and AdS spacetime.
