His father was Henry Illingworth and his mother was Mary, daughter of Sir Isaac Holden. He studied law at Jesus College and was called to the Bar, Inner Temple in 1894. Whilst at Jesus he played rugby for the university, winning two sporting 'Blues' in The Varsity Matches of 1889 and 1890.
He served in the Boar War 1899 – 1902.
He became the MP for Shipley in the 1906 General Election and served as Parliamentary Private Secretary to the Chief Secretary for Ireland from 1906 to 1910. From 1910 to 1912, he was a Junior Lord of the Treasury under H. H. Asquith. In 1912 Asquith appointed him Parliamentary Secretary to the Treasury, a post he held until his sudden death in early 1915. He had been nominated to the Privy Council but died before he could be sworn in.
He married Mary Mackenzie Coats in 1907 and they had three sons. He died suddenly in January 1915 of typhoid fever.
Portrait - see JCWA/A/A39