后座议员（英语：Backbencher）是西敏制国会坐在议会后座的普通议员。后座议员既非执政党内阁成员，又不是在野党的领袖、发言人或影子内阁成员，因他们已占据前座，故称前座议员。后座议员通常是新当选或委任的议员，或已从政府退休的议员。

由于并非内阁成员或党内重要人物，后座议员在国会的地位及影响力稍低。但他们可透过参与国会各个委员会，渗入各范畴的立法进程。而且后座议员通常占据国会多席议席，集体行动下足以左右不受欢迎的政策推行或避免执政党内部分裂。

In Westminster parliamentary systems, a backbencher is a Member of Parliament (MP) or a legislator who holds no governmental office and is not a frontbench spokesperson in the Opposition, being instead simply a member of the "rank and file".

The term dates from 1855. A backbencher may be a new parliamentary member yet to receive high office, a senior figure dropped from government or someone who for whatever reason is not chosen to sit either in the ministry or the opposition Shadow Ministry. By extension, a backbencher is not a reliable supporter of all of their party's goals and policies.