The Septennial Act 1715 (1 Geo 1 St 2 c 38), sometimes called the Septennial Act 1716, was an Act of the Parliament of Great Britain. It was passed in May 1716. It increased the maximum length of a parliament (and hence the maximum period between general elections) from three years to seven. This seven-year ceiling remained in law from 1716 until 1911. The previous limit of three years had been set by the Triennial Act 1694, enacted by the Parliament of England.

The Act's ostensible aim was to reduce the expense caused by frequent elections. It did not require parliament to last for a full term, but merely set a maximum length on its life. Most parliaments in the remainder of the eighteenth century did indeed last for six or seven years, with only two lasting for a shorter time. In the nineteenth century, the average length of a term of the Parliament of the United Kingdom was four years. One of the demands of the mid-nineteenth century Chartists—the only one that had not been achieved by the twentieth century—was for annually elected parliaments.

The Septennial Act 1715 was amended on 18 August 1911 by section 7 of the Parliament Act 1911 to reduce the maximum term of parliament to five years.

The Fixed-term Parliaments Act 2011 repealed the Septennial Act 1715 in its entirety.