"A bill or joint resolution that has been vetoed by the President can become law if two-thirds of the Members voting in the House and the Senate each agree to pass it over the President's objection. The chambers act sequentially on vetoed measures; the House acts first on House-originated measures (H.R. and H.J. Res.) and the Senate acts first on Senate-originated measures (S. and S.J. Res.). If the first-acting chamber fails to override the veto, the measure dies and the other chamber does not consider it. The House typically considers the question of overriding a presidential veto for an hour, with time controlled and allocated by the chair and ranking member of the committee with jurisdiction over the bill. The Senate usually considers the question of overriding a veto under the terms of a unanimous consent agreement."
CRS Report for Congress, RS22654