Government & Parliament
Archbishops of Canterbury have been members of the House of Lords by virtue of their office since parliament first began many centuries ago. In today's Lords there are two types of member - the Lords Temporal (usually known simply as Peers) and the Lords Spiritual (the two archbishops and 24 most senior bishops of the Church of England). The Archbishop of Canterbury is the most senior member of the Lords, being the first member entitled to take the oath of allegiance at the start of a new parliament after the Lord Speaker.
See further information on the Lords Spiritual and the Church of England in Parliament at the Church of England website.