Background
Southby was the son of John Southby of Carswell Manor in the parish of Buckland in Berkshire (now Oxfordshire) and his wife, Elizabeth daughter and heiress of William Wiseman of Steventon in Berkshire (now Oxfordshire).
Southby was the son of John Southby of Carswell Manor in the parish of Buckland in Berkshire (now Oxfordshire) and his wife, Elizabeth daughter and heiress of William Wiseman of Steventon in Berkshire (now Oxfordshire).
His father was Member of Parliament for Berkshire. Southby matriculated at Lincoln College, Oxford on 14 May 1641 aged 17 and entered Grays Inn on 4 November 1646. In 1660, Southby stood unsuccessfully at Berkshire for the Convention Parliament.
He was elected Member of Parliament for Berkshire in 1679 and sat until 1689.
In 1696 he was High Sheriff of Berkshire. Southby married Katherine, daughter and co-heiress of Robert Strange of Somerford Keynes in Wiltshire and they had nine children.
He died in 1704 and was buried at Buckland.
Habeas Corpus Parliament]
In 1659, Southby was elected Member of Parliament for Cirencester in the Third Protectorate Parliament.