1715: 1 George 1 Stat 2 c.38: The Septennial Act

1715: 1 George 1 Stat 2 c.38: An Act for enlarging the Time of Continuance of Parliaments, appointed by an Act made in the Sixth Year of the Reign of King William and Queen Mary, intituled An Act for the frequent meeting and calling of Parliaments.

Note: The year is sometimes given as 1716.

Whereas in and by the Meeting of Parliament Act 1694 it was, among other things, enacted, that from thenceforth no Parliament whatsoever, that should at any time then after be called, assembled, or held, should have any continuance longer than for three years only at the farthest, to be accounted from the day on which by the writ of summons the said Parliament should be appointed to meet: And whereas it has been found by experience that the said clause hath proved very grievous and burthensome, by occasioning much greater and more continued expences in order to elections of members to serve in Parliament, and more violent and lasting heats and animosities among the subjects of this realm, than were ever known before the said clause was enacted; and the said provision, if it should continue, may probably at this juncture, when a restless and popish faction are designing and endeavouring to renew the rebellion within this kingdom, and an invasion from abroad, be destructive to the peace and security of the government: Be it enacted by the Kings most excellent Majesty, by and with the advice and consent of the lords spiritual and temporal, and commons, in Parliament assembled, and by the authority of the same, that this present Parliament, and all Parliaments that shall at any time hereafter be called, assembled, or held, shall and may respectively have continuance for seven years, and no longer, to be accounted from the day on which by the writ of summons this present Parliament hath been, or any future Parliament shall be, appointed to meet, unless this present or any such Parliament hereafter to be summoned shall be sooner dissolved by his Majesty, his heirs or successors.

Source: Wikisource.

Further reading: Wikipedia.