Wentworth-Fitzwilliam was the second son of Charles Wentworth-FitzWilliam, 5th Earl FitzWilliam and his wife, Hon. Mary Dundas. He was educated at Eton and Trinity College, Cambridge, where he graduated MA in 1837. Two years earlier, his elder brother had died without issue, and he became heir to his father´s estates and took the courtesy title Viscount Milton. He became Member of Parliament for Malton in 1837. Holding the seat until 1841, he later reclaimed it in 1846 and then sat for Wicklow from 1847 until 1857, the year he inherited his father's earldom.
He held the command of the West York Yeomanry Cavalry for 40 years, from 1846-1886, and was a Yeomanry Aide-de-camp to Queen Victoria 1884-1894.
In 1857, Lord FitzWilliam was appointed Lord Lieutenant of the West Riding of Yorkshire, and stayed as such until 1892. He was appointed a Knight of the Garter in 1862, and was the senior knight at the time of his death. He died at his residence Wentworth Woodhouse, in Rotherham, 20 February 1902. As his eldest son predeceased him, his titles passed to his grandson, William.
Lord FitzWilliam was a keen sportsman and continued fox hunting throughout his life. http://en.wikipedia.org/wiki/William_Wentworth-Fitzwilliam,_6th_Earl_Fitzwilliam