Which particle carries electric current through a metal wire?

Electrons carry electric current through a metal wire.

Metals contain atoms arranged in a lattice, with some outer electrons able to move through the material. When an electric field is applied, these conduction electrons acquire a small average drift velocity, producing electric current. Their random thermal motion is much faster, but it does not create a net current because it points equally in all directions.

The conventional direction of current is defined as the direction positive charge would move. In a metal, that direction is opposite to the electrons' drift because electrons carry negative charge. This convention was established before electrons were identified and remains standard in circuit diagrams and engineering.

Protons remain bound inside atomic nuclei in an ordinary metal wire, and neutrons have no net electric charge. In electrolytes, plasmas, and semiconductors, other charge carriers can also contribute to current, so the answer depends on the material.