Third Party Candidate Law and Legal Definition
Third-party candidate is a candidate who does not belong to one of the two main US political parties, the Republicans or the Democrats.
It can also include independents and write in candidates. The United States has had a two-party system for over a century. Following Duverger's law, the winner take all system for presidential elections and the single-seat plurality voting system for Congressional elections have over time created the two-party system.
No third-party candidate has ever won the Presidency, but they have may strongly influenced the election results.