Mowbray was the son of Robert Stirling Cornish, and was educated at Westminster School and Christ Church, Oxford.
In 1847 he married Elizabeth Gray, the sole heir of George Isaac Mowbray of Bishopwearmouth.
The same year he assumed by Royal licence the surname of Mowbray in lieu of his patronymic to reflect the large fortune he married into.
Together, they had three sons and two daughters.

In 1853 Mowbray was elected to the House of Commons for Durham, a seat he held until 1868, and then represented Oxford University from 1868 until his death in 1899.
In the House, he was chair of the Committee of Selection and of the Standing Orders Committee.
He served as Judge Advocate General under the Earl of Derby from 1858 to 1859 and under Derby and later Benjamin Disraeli from 1866 to 1868.
He was admitted to the Privy Council in 1858 and in 1880 he was created a baronet.
From 1898 until his death the following year Mowbray was Father of the House of Commons.

A bronze bust was erected as a memorial in the House of Commons in 1900.
Mowbray was the son of Robert Stirling Cornish, and was educated at Westminster School and Christ Church, Oxford. In 1847 he married Elizabeth Gray, the sole heir of George Isaac Mowbray of Bishopwearmouth. The same year he assumed by Royal licence the surname of Mowbray in lieu of his patronymic to reflect the large fortune he married into. Together, they had three sons and two daughters.
In 1853 Mowbray was elected to the House of Commons for Durham, a seat he held until 1868, and then represented Oxford University from 1868 until his death in 1899. In the House, he was chair of the Committee of Selection and of the Standing Orders Committee. He served as Judge Advocate General under the Earl of Derby from 1858 to 1859 and under Derby and later Benjamin Disraeli from 1866 to 1868. He was admitted to the Privy Council in 1858 and in 1880 he was created a baronet. From 1898 until his death the following year Mowbray was Father of the House of Commons.
A bronze bust was erected as a memorial in the House of Commons in 1900.
Sir John Mowbray, 1st Baronet