William Leigh Brook was born on 17 December 1809, the son of James Brook and his wife Jane (née Leigh), and was baptised on 6 January 1810.
He married twice — firstly to Charlotte Armitage, daughter of Joseph Armitage of Milnsbridge House, on 20 May 1840 at Huddersfield Parish Church and then to Charlotte's half-sibling, Emily Armitage on 7 June 1850 in Denmark. He had five children from the two marriages:
The Leeds Mercury (31/Dec/1842) reported that Mary also had a still-born son, born on 22 December 1842.
He was involved in the formation of the Huddersfield and Manchester Railway and Canal Company and was a director of the board until the company was amalgamated into the London and North Western Company. He cut the first sod "of the intended railway from Huddersfield to Manchester" in October 1845 at a low-key ceremony held near Whitaker Bridge.
He was made a magistrate of the West Riding in 1849.
He laid the foundation stone of the Odd Fellows' Hall in Meltham on Monday 21 April 1851.
In 1853, he offered to partly fund the construction of a new road between Honley and Meltham, as the steep descent of Knowle Lane from Knowle Top down into Meltham Mills had resulted in a number of accidents and deaths.
In January 1855, he wrote to the Huddersfield Chronicle regarding the "dangerous state" of Thickhollins Bridge and reported that he'd alerted the local surveyors.
In August 1855, he left with his wife to visit "the principal cities and baths of Germany". The couple briefly stayed in Basel, Switzerland, where there had been a recent outbreak of cholera. By the time they reaches Frankfurt, Mrs. Brook was showing symptoms of the disease and died on the evening of their arrival. On receiving the news, William Leigh's brother Charles and brother-in-law Edward Armitage set off to Germany and arrived around the same time as he died on 20 September in Cologne, having also contracted cholera. He was aged only 46.
On the day before he died, he had written out his Last Will and Testament.
A memorial service was held at St. James, Meltham Mills, on Sunday 30 September by the Rev. E.C. Ince.
When the infant Charles Armitage Brook died in 1856, the question of how his share of the the inherited estate should be distributed became contentious, leading to a court case in 1857.
William Leigh Brook's second marriage to his sister-in-law in a foreign country had been highly controversial — had the marriage taken place in England, it would have been unlawful. The question for the court to decide was whether or not the marriage, which was legal in Denmark, was therefore valid in England. If it was, then Charles Armitage's share could be distributed amongst all the surviving children.
Eventually Sir John Stuart judged in April 1858 that Danish law could not be applied to the marriage of two British Subjects, and that the marriage was void and the children of the second marriage were illegitimate.
A further appeal was rejected in 1861 by the House of Lords.